I actually liked FO3's original ending, it was the Broken Steel retcon I found stupid; it didn't even make sense.
And what do you mean 'pay to play'? They could always do like in FO:NV and put a warning at the 'point of no return' although personally I think that kinda ruin the surprise.
In Daggerfall and Arena you could not play after you finished the MQ, infact in Daggerfall (although it has many endings, all of them happen at once and are considerd canon as far as I know);
I liked Broken steel, it added world changes after you ended the main quest.
They also added some new enemies, you have to love packs of ghoul reavers, or even more fun attacking a group of hellfire troops and find you are followed by a pack of albino radscorpions, suddenly the game was not easy anymore
In Daggerfall the game had multiple endings, however you could continue and the only difference between the endings was some relation boost with factions and perhaps some gifts who was minor for a high level Daggerfall character.
Fallout 1 and 2 ended then you finished the main quest as I understand, Fallout 3 followed this and the suicide mission was a plausible way to end the game. None of my characters was willing to go that route but relied on the Oasis fallback plan
Main quest appears to be pretty short 20 hours as I understand, however Oblivion main quest was also pretty short if you did it all in once and dropped Allies for Bruma.
My main concern is that dragons goes away at the end so you delay it to get all the dragon shouts the same way you waited with finishing the main quest in Oblivion to have access to sigil stones.