This is something I'm exploring with Summer of Roses.
Corbynsceptisim in the PLP would be an issue, but my instinct is that Labour MPs will be so gobsmacked with the fact Labour came out ahead, as even some of his fierciest internal critics were in 2017 even in that defeat, that they don't try to torpedo his premiership, at least not by defying the whip on a confidence-related bill (yet). That's the rebellious PLP dealt with (for, say, a couple months before the experience wares off).
As for the Lib Dems, I agree with Gary that it's political poison for them, and they know this, so they're off the table for now. The SNP would not accept a coalition, I don't think Labour would either, and it'd on the whole be quite weird for an outwardly separatist party to be given, say, a ministerial position. Confidence and supply with the SNP, then, with one of two major concessions: Devo Max (e.i.; Holyrood gets it's long-coveted tax-raising powers) or a second indy ref.
I think, personally, that Labour is in a strong enough position (and, depending on where Labour's extra seats come from, the SNP in a weaker enough one) that Labour could reject a 2nd ref and instead give them Devo Max. This allows the SNP to rebuild their support base from within Holyrood. Needless to say, this deal would be very much controversial with Scottish Labour MPs and the fundamentalist wing of the SNP, but I think with enough arm-twisting they'd get on board; Labour has a very clear gain in terms of getting into government, the SNP could in theory refuse to help them, and hope that the chaos makes indy more popular. But one has to wonder whether those many Central Belt voters - who had only been voting Labour religiously until, what, 2 years prior? - would feel betrayed by the SNP preventing a progressive government. I reckon they would, or at least, I reckon Labour and the SNP's strategists' would both think so, and I think that threat would get the SNP on board along with Devo Max.