How about increasing the rate that Realm Loyalty falls depending on that realm's density? This is sort of a different approach to the above idea regarding harder TOs, but with the same goal in mind.
However, one thing I'm concerned with is that this might too heavily force players to clump in big, monolithic realms. Smaller realms will lose even more players in favour of bigger realms, and newer realms won't be created. From what we know of Atamara and the CE block, a healthy amount of the player population favours safety over risk, even if it means boredom over fun.
