Plus you could still continue working in X3. I usually finish projects in the version I started them on.

I have gone through all versions since Home Studio, S6-7-8.5 skipped X1 and X2 a then X3 and now Professional. 
ALL my CWP files open and they all have played. If I open an old CWP from S7 which was 32 bit and a different interface I get the missing plug in warning. They still open and the missing plug ins will show in brackets in the effect bins. Just delete and replace with a new one. 
You get a warning on opening about what has changed, that's all. Midi is Midi , audio is audio. 

Cactus Music
I have gone through all versions since Home Studio, S6-7-8.5 skipped X1 and X2 a then X3 and now Professional. 
ALL my CWP files open and they all have played. If I open an old CWP from S7 which was 32 bit and a different interface I get the missing plug in warning. They still open and the missing plug ins will show in brackets in the effect bins. Just delete and replace with a new one. 
You get a warning on opening about what has changed, that's all. Midi is Midi , audio is audio.

 
It works both ways too, i.e. backward as well as forward compatibility. Projects created in a later version can normally be opened in an earlier version.

Yes Kev, but certain features added in later versions, for example ProChannel, Melodyne, will not work