I am interested in the point about Anglo-Saxons fighting for the Byzantine Empire in Albania being seen as implausible. This is in fact very close to what happens in The Last English King (1997) by Julian Rathbone. It is historical fiction rather than alternate history, but all the same, some publisher felt it was a legitimate approach that readers would accept.
This does bring us back to how far historical authors have to 'defend' their choices, especially if they are based on actual history, from accusations of implausibility by readers. I guess it is tougher still for alternate history authors.