Now that we know players from other factions can join the same guild, will there be an option for multi-factional guilds to promote certain officers as regional leaders, i.e. leaders of that particular faction? I can't see one leader organizing events for all three factions.

Its already possible.

I dont honestly see anything bad about this.. its game after all. In order to play on every faction, you need to level up 3 character, Im sure most have time for only 1 though. Last thing what devs want to do is to make communication between guild members harder, people have made alts for other factions all the time, so why they need to find another guild.

Best thing about multi-factional guilds is imho, maybe now guilds start to play other factions together and spend more time in the game. We all know HC guilds finish endgame in less than 2 month, if they move to another faction thats only good.

Umm...You can play the faction content for all three factions from one character--When you get to level 50, you play the next one as 50+ (higher difficulty), and when you've finished with that, you move on to the third as 50++ (even more difficult). You won't see or interact with the actual faction members during that time, but you can play the content. The only reason to make alts for the sake of faction content is if you don't want to play it at the higher difficulties.

I know, but maybe try different races and classes and play together with your guild mates when you see everyone is online?

Multi-factional guilds are just pure convenience for players and Im glad they allow it.