Shouldn't we all transfer to a new World when I think about it ?
I mean, we got those who care about WvW and those who don't.
So technically, it wouldn't change much for those who don't WvW, thus we wouldn't be a fractured multi-World guild in the end, right ?
Am I right ?
First off, just to get it out of the way, GAFGuild will not be moving its home server. I wouldn't want to even if it was my call, but it's not anyway- it's off the table.
There are a few things you need to consider though:
The bit about "those who care about WvW and those who don't" is a kind of false dichotomy. I don't think you could divide this guild into those two categories at all. It's a little reductive to imply you either care about WvW- and thus want to transfer to a consistent tier 1 or 2 server with many hardcore WvW guilds- or don't care about it, and thus don't care what server your on. I
love WvW, especially in concept and when considering its potential, but I didn't particularly love the matchups that we tended to rotate through and the tactics we seemed to encounter with frequency when bouncing around tier 1. To me, WvW is not hardcore dedicated PvP... it's something pretty unique. It's filled with inherently unfair elements. There are hybrid PvE events and jumping puzzles. It scales you up so that you can make an impact at level 1, but you can level up in it too. The state of the game can change dramatically while you're asleep. There are force multipliers at every turn. It's
awesome, but it's not the kind of gameplay that I want to be really gung-ho about competing at the highest echelons in. I really wouldn't mind playing against some servers that don't take it quite as seriously. It would be great from my perspective if we wound up in a matchup where a small GAF team could really run the table on a map that we'd get obliterated on in Tier 1. Other players feel differently about this and that's beyond fine- the beauty of the game's architecture is that it'll make little practical impact for them except for WvW, and we can even make them remote influence operators so they won't altogether lose out on the guild bonuses in the crossfire. That aspect alone makes it simply not that big a deal.
Something else to consider is the fact that we have an awful lot of members of various levels of activity. We're at around the 300 mark last I checked. It's quite honestly a tiny minority that regularly post on these forums. Attempting to coordinate a mass exodus solely for the purpose of remaining where the hardcore WvWers are just doesn't really align with our philosophy. If even a handful of people happen to not be playing and keeping up with our plans for a while, I want them to know that when they log back on, SBI is still our home- not find themselves stranded and forced to cough up some gems to transfer.
Also, bear in mind that the overwhelming majority of people transferring for WvW-related reasons are doing so to high-to-full servers. Hoping that we can get each and every one of our members over to the same one without us hitting a cutoff is incredibly risky and there would be no way to know if we could fit without trying. It's a much better solution in my eyes for individuals to make their own decisions about what's best for their gameplay experience and the possibility of joining a secondary guild for WvW only and guesting with us for everything else. That way they don't have to all go to the same server either if they don't agree on a "correct" one.
Finally, I just want to stress that we've never positioned GAFGuild as a hardcore WvW (or hardcore anything) guild. There was a ton of deliberation about what server to land the guild on, but WvW ranking didn't factor into that discussion at all (and in fact SBI was Tier Pathetic or something around the time we made the decision). We had no idea what would happen. The surreal bit is that this entire scenario wouldn't really be relevant to us as a guild except that SBI just happened to be ridiculously successful in WvW and regularly ranked at the top. Again, while it would be tragic for the people who were into hardcore WvW to be cut off from that experience and forced between choosing that versus the ability to stay in the guild, guesting makes that a complete non-issue.
Guilds are World-based ? Doesn't change if leaders transfer ?
Weird system.
It doesn't matter which members of which ranks are on which servers so much as you can only spend influence on the server you're on. So the guild members on other servers can earn and spend their own influence (at a slower rate than us of course)

We do already have guild members on other servers even without Guesting; it's not a requirement to be on SBI, but SBI is our home.