If Richard II dies at the same time as his older brother, once Edward III dies in 1377, who is the new monarch? I would presume Philippa, were they accepting of queens by that time? Or would John of Gaunt have a chance? Or, since he never rebelled against Richard II OTL, perhaps he agrees to accept her with some sort of promise to give him some power (or just to support him in his attempt to take Castille)
And, if Philippa, how long till it passed to Philipp's son, Roger? Her death date on Wiki is given as 1382 but in Roger's article it's 1378. it seems either way, john could become regent anyway.
What would Queen Philippa be like versus the French? Would she press English claims quickly? (Hmmm, perhaps she might even push them harder than others would to prove she had what it took to be a powerful monarch.)