Well, Hungary would unfortunately still be shackled to Bohemia, but it could work. The boy would probably be Lajos/Ludvik after Marie's father, or Karel/Karoly after Sigmund's.
Or Ladislaus, Sigismund was a big fan of Saint Ladislaus.
Other than that, I couldn't really say. But I agree with
@Svetonius21, if Jadwiga dies without issue, or with only a daughter, Marie's son (or rather Sigmund probably) will put in a claim to the Polish crown. If Sigmund and Marie have 2 boys, I could see a younger son marrying Jadwiga's daughter in a peace treaty. Now we have the house of Luxemburg ruling over the Empire (or do the electors decide they prefer the Wittelsbachs?), and a stretch of territory from the Baltic to the Black Sea. Just for the irony points, name the boy after Sigmund's dad, and we get a TTL Holy Roman Emperor Karl V with a huge unmanageable empire
That's unlikely, Sigismund is was overstretched (Hungary, Bohemia, HRE, sometimes in Italy) to expand even more in Poland, not to say that he was always indebted due to constant warring.
Indeed, the only time he moved against Poland was pretty much a ruse to get money (which he succeeded).
Now we have the house of Luxemburg ruling over the Empire (or do the electors decide they prefer the Wittelsbachs?)
That's a good observation, there is no certainty that Rupert of the Rhine would die on schedule, though his authority was restricted to the Rhineland, it could establish a Wittelbach-led anti-Luxemburg faction with 4 electors backing against Wenzel and Sigismund, and even if Rupert bites the dust there is still the whole deal with Jobst of Moravia, maybe with Mary alive (and later his son and heir) she could represent her husband in Hungary and prevent the whole chaos his long absences.
Albrecht wasn't crowned emperor IIRC, although he was elected German king - which is sort of the same thing (I think).
Romanorum Rex (or Teutonicorum Rex, King of the Germans) was the title of the elected German king still to be crowned by the Pope, in the beginning it meant that the guy wasn't a true Emperor and could be subjected to Antikings and other issues, over the time, as Imperial Authority in Italy and Burgundy declined and Charles IV excluded the Pope from the Imperial Election, the title became synonymous with the Emperor, as the title and authority was pretty much restricted to Germany anyways, in the end it's just semantics.
Albrecht wasn't the first Habsburg emperor - that was Rudolf way back when - and Friedrich III was Albrecht's kinsman (cousin/uncle), and the "Luxemburg" blood only arrived in the Imperial Habsburgs with the double marriage between the Hungarian Jagiellons and the Habsburgs.
Actually, Rudolph was just King of the Romans as well, so was his son Albert, Friedrich III was the first Habsburg Emperor to be crowned by the Pope.
So we could see a side line of Habsburgs ruling a kingdom of Naples (unlikely, but still an awesome idea) instead of Giovanna causing civil strife between the Aragonesi and Angiovesi supporters by adopting first one heir then a different heir, and both trying to claim they're legitimate.
Now that would be awesome.
Well, Sigmund wouldn't be "ruling" Hungary here (Marie would, though IDK how the Hungarians felt about her), and after Marie, their son. So whether Sigmund is popular in Hungary might not factor into it. Plenty of sovereigns have had unpopular consorts and weathered the storm.
Mary was a non-actor in Hungary, the authority was all on Sigismund's back, hence how he got the throne after her death, it's true that he was unpopular, maybe with Mary alive he could get some extra legitimacy, maybe the war with Ladislaus of Naples either don't happen or don't get as much traction from all the magnates (some may flock under Mary's banner).