It seems there'll either be new ships or new ranks added, I think the devs have confirmed yes to both.
Not really bothered about crew myself, for me a new rank is 'ok what cool ship can I sail now????'. The jump to master and commander lets you have a surprise or renommee which are considerable upgrades over the slobodan so it's all good.
One thing that does strike me as a bit odd as at Post Captain/the rank you can sail the frigate, belle poule or the trincomolee but it seems in every single aspect the trinc is a straight upgrade. I'd imagine when the production of trincomolees catches up with demand, frigates/poules will be pretty scarce. Sounds like another rank is planned to slot in there.