Battlegroups are unlikely to be assigned, however we will probably end up setting up "localized hubs of activity" within the TEST galaxy from which we can pull personnel for response fleets.
There will also probably be squads that focus on specific playstyles, similar to TEST Alliance's Romeo Squad, Sperg Squad, Predditors, etc.
Except that we're not putting these groups together by force - we'll let it naturally happen when PU Alpha spools up. So keep your ideas under your hat for now, and when PU Alpha starts up, we can start discussing how we'll be structuring things. Montoya probably has some ideas of his own, as well. The PU Alpha and Beta phases will be a time for us to put our ideas, squads and doctrines to the test, as well as iron out how we'll be moving forward in the final PU release.
The rule #1 in TEST is to not take everything seriously, though when it's go-time, serious business ensues. I'm hoping the Combat Information Center module that Foundry 42 is working on will enable us to effortlessly structure the fleet in-situ without needing some form of external organizing work.