Virtually none I'm afraid. It's exactly because 1.0 was being shutdown and replaced, that they could afford to add things like that which normally would completely interfere with the normal flow of the game.

Also the "enemies invading the three cities/aetheryte camps" was actually also for pragmatic reasons - it was no coincidence that these were places that players tended to idle at, and given 1.0's awful server structure and zone design, if there were more than a certain amount of players in a particular area it would cause severe lag or even crash the game.

It was so bad the Inn Room in Ul'dah was completely broken due to Ul'dah being the 'endgame' meeting place in 1.0, which SE never was able to even fix - they ended up putting in a work-around by using a back door (from a NPC near the fountain under the Husting's Strip) to enter it right up to the end of service. Thus the enemies pouring into the cities like Ul'dah was to actually force players out of them and to not idle there for long periods.

Hence I don't see this ever happening again I'm afraid. It was literally one of those 'once-in-a-lifetime' things that will never be repeated sadly.