Marrying into the (current and not necessarily long-lasting) Imperial family was not seen within the Roman elite as having any potential Imperial possibilities for a 'barbarian' non-Roman in the C5th. Even marrying into the fairly long-lasting one of the capable if harshly orthodox Christian persecutor Theodosius 'the Great' ( d 395 aged only 47 so a good subject for 'What Ifs' where he lasts longer) did no favours for the Visigothic leader of 411-16, Athaulf the younger brother and successor of Rome's 410 sacker Alaric. He forcibly married the daughter of Theodosius and half-sister of current, incompetent Western emperor Honorius , Galla Placidia - who Alaric had carried off from Rome as a hostage after the 410 sack - in 415, at that point had a fairly strong German army led by his Goths, ruled a regime set up by his migrating army/ tribal group in NE Spain and SW Gaul based on Barcelona, and was said to have aimed idealistically at a fusion of Romans and Goths as symbolised by the marriage. The recovering Western Roman govt and army, now headed in effect by Honorius' new strongman general Flavius Constantius, continued to make war on him and he had no major Roman backing, and he was soon assassinated in his stables by a rival of his family in a personal blood-feud; his heir Wallia then faced FC's army and settled for a peace-treaty whereby he handed Galla Placidia back and became Roman 'foederatus' vassal-king of Aquitaine. FC then married GP himself - and they were the parents of Valentinian III, who succeeded Honorius as a small boy in 423/5 (a usurper ruled Italy immediately after H died in 423 and was removed by the Eastern Roman army in 425) under GP's regency.
Given Attila's reputation for bloodthirstiness and extortion as well as the fact that the Huns were not even Christian unlike the ('heretic' Arian) Goths in the 450s, Attila - or a son of his by Honoria - would have been even less acceptable as a potential Roman ruler or strongman in his wife's or son's name in the 450s or 460s, and as far as is known his main interest in Honoria was as a political addition to his ability to meddle in Roman affairs and extort money and land. (When the Eastern empire's chief minister tried to get rid of him by bribing potential assassins in 448, and this was discovered, Attila did not exact bloody revenge except on the plotters and in stead forced the embarrassed Eastern envoys sent to negotiate to offer him a huge pay-off which he accepted; he was far more cool-headed than his reputation suggests.) He might well have tried to demand Gaul as a new home for his people, given its fertility and usefulness for his cavalry and his pastoral nomad tribes, and/or another huge pay-off as the 'bride-price'; and if this was refused, which was likely given the reaction of the local Roman and Gothic elites there who had the military power to defy any orders to give in by the weak Western govt, we get an equivalent of the 451 invasion and battle. If Valentinian tries to give in to Attila, no doubt against the advice of his military supremo Aetius who had past experience and many friends in Gaul from campaigning there, we probably get an earlier version of the OTL clash between V and Aetius in 454, when Aetius was supposed by jealous, genuinely alarmed, or lying courtiers to be after V's throne (V had no son) for his own teenage son and V murdered him. Aetius' allies then murdered V in reprisal. Does Aetius overthrow Valentinian, who was not much good at political or military matters, and take over the West as a far more competent and probably successful leader - and with his Gothic allies' help defeat Attila, stave off the Vandals in N Africa with Eastern naval help, and set up a more successful dynasty in a smaller but viable Western empire? (The rule of Aetius and his family after 455 is one of my own main Roman survival PODs in my Alt Hist of Rome books.)
Attila could have moved into N Italy from Pannonia (W Hungary) to put pressure on the Western Empire to accept his terms, either with Honoria as his wife after she ran away to his court or in order to get a treaty signed giving her formally to him plus a dowry of provinces (a slightly altered version of OTL 452), and then stayed longer to keep the Western regime in fear of him and to see that the terms were carried out - and used the plains of what is now E Lombardy to feed his horses and settle a body of Hunnic or allied warriors as 'foederati' within Roman Italy. But he could not stay too long in Italy himself, even if there was no plague to make withdrawal safer (as probably occurred in OTL 452), in case of revolt by his own subject tribes in the middle Danube basin -which the Eastern empire would probably stir up. If Valentinian gave in to his demands, he might well face removal by Aetius and a mixed Romano-Gothic 'hard line' faction, then war with both East and West of the Roman world. The previous attempt by a major 'barbarian' warlord with a war-ready army to blackmail the West into accepting him as a leading figure in its regime had been Alaric the Goth in 408-10, who had been intimidating the militarily weak Honorius after a purge of the Western army (involving the killing of ex-regent and half-German commander in chief Stilicho in 408) had left the West without a viable army leadership to resist the Goths; this ended with Alaric getting fed up with Roman double-dealing and setting up his own puppet emperor, renegade senator Attalus, and sacking Rome. The idea was for Alaric then to rule behind the scenes as commander in chief of the army (magister utriusque militiae), as Stilicho had done for Honorius when H was a boy. Attila could try to do the same, but would then face either an escaped Aetius or one of his generals (eg Aegidius, later ruler of NW Gaul, or future OTL emperor Majorian) plus the Goths and Romans in Gaul/ Spain invading Italy, or else an Eastern invasion. Given that he had to hold onto his own huge overlordship in central Europe (more of a personal leadership by fear/ force than an 'empire' as not institutional) and his Huns were unused to the Mediterranean climate, Attila would probably have had to collect his loot and retreat to the Danube or face defeat, which would be aided by disease and defections.
In this era of personal command and establishing power by charisma and luck/ skill among the Roman and non-Roman leaders, with cultural identities and army/ tribal membership fluid, the potential for an unexpected - if lucky - leader to emerge as founder of a long-term 'state' is immense; my own favourite is for a repeat of the Roman 'personal leadership reverses so called inevitable decline' carried out by the mid-C3rd Roman emperors, eg Claudius II 268-70, Aurelian 370-75, Probus 276-82, Diocletian and Maximian 284-305, and Constantine 306- 337. The Empire, even the weaker West, had the advantages of a long-lasting institutional and cultural/ economic basis for stability , despite the huge problems of a feuding, often petty-minded elite and the tax-dodging, selfish rich (lessons for the present day UK??) . So this gives major assets to a luckier Flavius Constantius, leader of the post-410 Roman revival (d 421, probably in his forties), Aetius, or Majorian in rallying the Western empire - and Aetius had lived among the Huns as a young exile in the 420s and had the talent to lead Goths as well as Romans vs Attila in 451, so he has the best potential in this.
