I have no plans to write CWB converter. I see no reason for that. Cakewalk (CbB, old Sonars and I guess next Sonar) can convert CWB into CWP (unpack).
I can only repeat, install CbB (free) or use original Sonar and convert CWB into CWP.
Then you can open the result in REAPER with ReaCWP.
Note that in case you have Cakewalk specific features in your projects, it make sense to "simplify" projects in Cakewalk before conversion. So probably that will be iterative process: open in REAPER, check what is far from perfect, fix in Cakewalk, check the result, may be repeat the cycle.