I remember when the forum was last changed to it's present format. The update was reasonably seamless and the format change seemed like a step in the right direction at the time. At that time there was no problem with keeping all the old posts, and everyone could keep their names and their details, and threads seemed to remained relatively intact. I've no objection to a change, although you haven't explained why this is the most critical question to be answered at this time. Is the Forum hosted on the Cakewalk servers? If so, are they being shut down now that Bandlab has acquired Sonar?
If it's just a question of putting the forum onto Bandlab's servers for ease of functionality then I have no problem with that.
As you've quite rightly noted, the forum here is a big part of the Sonar world and I hope that community is of value to Bandlab and is worth keeping. I don't know much about this part of Cakewalk, but I'm sure there is great Forum software out there and "a change is as good as holiday" so they say. Please be aware that the Cakewalk community is going through more of a "leave of absence" rather than just a holiday at this point in time, so I for one would like the change to be as seamless as possible. I will leave this most important decision in what I am sure is your capable hands and look forward to the future. Good luck with your venture going forward.