I've been barking up and around this tree for a while now. Through various DAW rebuilds, an OS upgrade, and general housekeeping, I sometimes run into problems with different versions of synths and plugs not getting recognized. I've wished for a long time for better asset tools, especially the ability to skim preset info out of a project file so you can more easily "swap" the offending plug.
 
When on load if SONAR finds a missing synth/plug and can't load it, it would be great to be able to re-assign it at that point. So, for example, my Pro-52 is all bunged up from an older project and it barfs on load, I could simple point it to Pro-53, where patch info should load just fine. Great, right? :-)
 

Yes please!  This would be amazing, although from a programming point of view, I have no idea how difficult it would be to integrate into a patch or something.  I'm guessing the answer is that it would be really freaking difficult, but hey, lets hope I'm wrong.

Yes please!

Please!! Please!!!

It should do this:
 
Sonar can't find this plug -> user can browse for it -> Sonar registers it on the fly -> user sees plugin as expected.

Obviously somewhere in Sonars code it knows what plugin and version of it are in the project, because it can tell you it's missing. It would seem that if Sonar points to one plugin it shouldn't be too hard to change that reference to another. Clearly I'm no programmer and I've no doubt over simplified something really complex. But have I.

Good idea, but there's no guarantee that the patch data saved in the cwp file for the old version matches that of the new, so SONAR could crash when trying to get the new version to load it (and people would blame SONAR :-)) or the sound/effect may be totally out of whack and unhelpful.

It currently opens a default plugin window with details of what it can't find, if it opened up your plugin list allowing you to select the plugins and open it giving you the chance to select a preset.

A while ago I suggested the idea of optionally embedding the plugins into the project, for instance by taking all the DLLs and compressing them into a single file that goes with the Sonar project. That way if you open the project 10 years later, you can recover the missing plugins from the project's plugin backup. However that creates all sorts of other issues, like the fact that some plugins are more than just a single DLL (they have full installers, extra files etc), licensing issues etc.
 
If you are talking about a synth like Pro-52, Sonar does have an option to swap it out with another synth, however that feature seems to be broken. If the synth you are trying to replace is no longer available, then the one you are replacing it with will be disabled in some mysterious way. I have not figured out how to enable the one you replaced it with. I gave up after a while and just copied the old synth's MIDI clips and FX to another track.
 
I don't think it would be possible to use preset data between different plugins, as they all store the data in their own format. When you save a project, Sonar asks each plugin to give it its current blob of data that will be used to restore it to the same state when you open the project next time. But this data is just a blob of meaningless data to Sonar, so unless there is some standard format developed, this will be not be portable.
 
Probably the best solution right now would be if you saved the Pro-52 preset and Pro-53 has the ability to import older presets.
 
BTW Sonar can swap out VST2 versions with VST3 versions of the same plugins, so there is some of that going on at least.

I realize doing a 1 to 1 replacement will probably never work. But what could be possible that would be very helpful would be to at least recover the name of a patch or preset that was loaded in the plugin. That way if it's an older project I'm coming back to I would at least have some idea of what I was doing in that track and could make setting a replacement up much faster.