Hi.
I have no idea yet what the plan is nor how far the pm2 version is or will be
But probably one of the main targets will be better performance in editor (which already has been improved compared to pm1.8- versions)
and backward compatibility.
Personally I would not mind if PM2 would not be backward compatibility, if it would be necessary to have greater improvements which would not be possible due to backward compatibility.
But I think many would still want to have backward compatibility
(maybe optional disable certain parts when updating a previous version project vs a new project)
Im not sure if 1.9.7 already supports 'enter play mode settings' (pre 1.9.7, there are known breaking issues with it)
But that would also be a mandatory, as when your project get bigger 'enter play mode settings' will speed up developing a lot.