It’s quite clear from the Release Notes thread that 1.8 is frozen, whilst there have been numerous releases of 2.0 since it was first released.
Agreed that most of these are fixes/improvements for ARC, but there have also been UI tweaks and stability fixes for Roon itself.
One major change that has already been delivered is Folder Browsing in Roon - this may or may not be relevant to you. Another major change that is currently being tested in Early Access is the Playlist Improver. Folks are already asking for this functionality to be extended to the Album Browser.
The decision on when or whether to move is of course yours to make, but there will definitely come a time when the move will be inevitable, because Roon Labs will drop 1.8 completely.
Edit: Playlist Improver is now in Production!