The Steam version and the non-Steam version are technically exactly the same installs and it doesn't even update the game via Steam (if you verify files within Steam it'll put all the old files back (about version 2.2?) and then when you ran the game again it'd redownload all the patches again!). You don't have to play it through Steam, you could just download it directly onto a computer without Steam if you desired:
NA:
http://www.finalfantasyxiv.com/playersdownload/na/
EU:
http://www.finalfantasyxiv.com/playersdownload/eu/
(Although both do actually link to exactly the same installer)
However, although you could log into that without actually installing Steam, your SE service account is still technically a "Steam" account and you can't change/remove that. It is literally just a flag on your account, but SE won't change it (or at least I've never heard of anyone reporting they changed it).
The only Steam limitations are that you (apparently) have to purchase Heavensward through Steam and can't purchase normal physical/digital version. I don't know why since you CAN do the digital collectors upgrade direct from the SE Mogstation without going via Steam (I did a few months ago) so it seems very unfair that they're forcing this limitation now. Some people are saying it's Valve forcing it, but I personally doubt that (no actual proof though, it just feels like an SE thing to me!).
Sorry I don't know if this was actually any help or if I've just made it more confusing :S Was just trying to clarify what Steam version is/isn't, but basically unless something changes with SE your account is tied to Steam indefinitely (even if you don't subscribe via Steam or install it). Sorry
