I don't know why you'd even think 8 would be the upper limit of a Free Company. This is supposed to be the equivalent of a guild in WoW, where you have a lot of people and go do content together. There's going to be content that supports 24 people so why would you have any less than that?

The forming of a Free Company also sounds like that of WoW, just with some different restrictions. In WoW, you needed 8 random people to sign your petition to form a guild. In ARR, you must have 4 people who have joined any Grand Company (i.e. reached level 20) to come together and form the Free Company.

If the system is designed well, that doesn't mean these 4 will be limited to being the only officers. You should be able to assign ranks like you currently do in linkshells. I expect the ranking to be something like founders > officers > members. If/when they make a FC bank or vault, you'll probably get access to certain tabs of it based on your rank. This is how it works in WoW anyway and I can't see them doing it much differently since it works.