As announced a few weeks before, we are sorry that we needed to split RF4 accounts and Steam accounts, but there was a lot of technical issues causing a lot of problems, so this decision was made. It wasn't an easy decision but sometimes that hard decisions need to be made.
We can't give you a 100% answer if there will be any possibility that RF4 launches players will be able to log in using s Steam in the future.
If you really want to get Steam achievements I would advise you to start a new account on Steam, as at this time, we are not able to transfer your existing RF4 launcher account to Steam account and we don't know if this will be ever possible in the future.
I hope this helps a bit.