I would love for the main cities to be hubs but another way i would like to see it go is:
If/when they implement Guild capitol ships they should become mini hubs for guilds. GTN terminal, mailbox, bank storage, training dummies and access to your ship. I also think that they should incorporate a way for your guild ship be the one that drops your guild off at OP/FP run planets via drop pods. No difference from the Ziost now but would add greatly to guild RP for those that do.
The fleet would then become a place for shopping and training. For example, I would still need to go to the fleet for purchasing gear with comms and training up my crafting and skills. For RP'ers this would also be a visit to the cantina or whatever their character would need to socialize with people outside of their characters (unit) guild. This is very similar to how a real life military unit would act.
I also think the players on the guild ships should see trade and general chat. This would be how the guilds would not completely segregate from the rest of the community and still allow un-guilded players a chance to find a guild or just communicate with guilded players, for grouping or advise. For immersion sake it could be considered reading the text on a terminal or whatever you could think up. I think this would be little difference to seeing the chat of whole fleet when your only in one spot and your hearing isn't THAT good. The guild ship terminal would be similar to a Galactic twitter of sorts.
We are already broke down into fleet instances when so many players are on fleet. This would aid in game performance for those with low fps due to player density. The chat is there, the players are there, just not the toons. So in the end, little would change for the community and get us all off that damn fleet like horses waiting to race.