People keep missing the point of legacy servers. We want it the way it was back then. Unless a change is strictly graphical or for performance(ie run on a newer client), the answer is NO. Most purist players are even refusing these. Others didn't like the fact that the login cap was removed on Nost. But Blizzard ran a cap strictly because their ancient 2005 hardware couldn't handle all the players that wanted to play. It's a safe assumption that if they could, they would have ran with higher logins as Nostalrius did, then simply tried to deal with the population by adding more mobs or reducing spawn times. Their solution was mainly to keep adding new servers, each which ran on their own hardware.
I hope that legacy servers do have some kind of cap though. 15k players online eats a dick. There aren't enough zones nor mobs in them to support all the players, and increasing mob counts or decreasing respawn times can only do so much. Questing on Nost was a fucking nightmare for months, and after that, it was always a nightmare to farm anything at 60. Yes you can fight the enemy faction, but half of the players are on your own side and just tag warring things you need. The population would be less of an issue in later patches that add more levels and zones, spreading out players more, but in Classic, WoW just struggles with this big a population. Maybe if they capped us up at 10k; that would have been enough. The rest could have started feeding a 2nd realm.