I installed the  latest version of Dimension Pro.  I have been doing most of my work in X1, but went to look at some old P5 projects.  When I did so, I got messages saying that Dimension Pro could not be found.  I am pretty sure I had inserted these as DXi. 

My question is, since DP  is now VSTi only, is  there anything in the installer which would have trashed the older DXi version?  I used DP on nearly everything, so it's a bit of a pain to have to re-insert all my instruments.

I believe that is true...I read that somewhere around here and it's not on my X1 anymore.  I haven't checked 8.5.3.

That's why I have not installed the latest DimPro update.  I have dozens of existing projects that include the DXi.