I was thinking recently about alternate first wife for Casimir the Great. IOTL he was bethroted to Bona of Luxembourg, daughter of John, King of Bohemia. This Piast-Luxembourg marriage was meant to solve issue of John's claims to Polish throne. John would ceede his rights to Bona, she'll marry Casimir and quarrel would be over. But after birth of his second son, John decided to keep his rights, because he wanted crown also for younger son, so bethrotal was broken in 1318 and John renounced his (already dubious) rights only after Casimir has paid him large sum of money . Ultimately Bona married John the Good, future King of France and had large brood of kids with him.
So if John of Luxembourg had only one son (say that would-be-Charles IV died as infant) it is possible that bethrotal would not be broken, Bona would marry Casimir (so no Aldona Anna) and had large brood of kids with him, not with John of France.