I did earn over 1,400,000 gold legitimately and it doesn't cap at 999,999.
Yep, I had about that much when I retired my first character. I kinda expected it to "roll over" or something when I hit a million but it just kept on going up. If it can do one million, I guess it's possible to get to at least 9,999,999 as well. I wonder if anyone's gone past that and can confirm that it's possible to hit the 10 million mark without it blowing a gasket.

I think it would work better at the end of the Civil war, if you replaced either Ulfric as Jarl of Windhelm, or Elisif as Jarl of Solitude (as she would then become High Queen)
Wouldn't work as becoming High King/Queen just tacks an additional title onto the one a Jarl already has - he/she doesn't give up their Jarldom to take the other job. Torygg was both High King of Skyrim and Jarl of Solitude until he died; I think it's even mentioned in the game somewhere that it has become the (Imperial approved) tradition for the Jarl of Solitude to be the High King/Queen as well. If Elisif were voted in as Queen she would still be the local Jarl; same with Ulfric in Windhelm. So unfortunately there won't be an opening for the Dovahkiin in either case. Then there's the fact that the Dovahkiin would have still have to qualify for the job by virtue of race (Nord) and, presumably, lineage as well. That in itself would make it a no-go for a lot of players.