I would think that unifying the federations would allow them to make sure the best teams are competing for titles. I don't know much about the financial situations, but I would think that unification would allow them to spread the wealth in terms of players, funds and fans. It should make for exciting competition.
I'm by no means a soccer fan, but don't you want to put the best team on the field that is possible? I would think that would involve players from all the federations, I get that there are superiority clashes between the groups but I imagine they all have something to offer for the greater good.
No, the four football federations in Great Britain should not be unified for FIFA tournaments, because the FIFA means more if people represent their own regions. Combining would make it more likely that the group would win, but how few people would be able to represent their countries then? It is better to keep the competition localized to each area.
There is absolutely no reason that I can think of for the four football federations in Great Britain to be unified for FIFA tournaments. Sure, some might say that it would streamline operations when it comes to FIFA but I think the reality is that it would be an expensive, bloated logistical hell.
I don't think the four big clubs in Great Britain should be combined. Think of all the bad blood there is between the different squads and their fans. I think that having four close teams that truly hate each other is a beautiful thing in terms of competitive spirit in sports.