That‘s even simpler than my previously suggested plugin architecture, but a bit more cumbersome for the end user (but an installer could simplify the process of copying the desired SimConnect.dll into the app directory).
Of course that solution would also be less flexible for the end user - unless the user exchanges the DLLs before (re-)starting the app.
Then again: how many users really use two sims „in parallel“, so this might more be an academic problem.
Of course that requires that the SimConnect.dll libraries are binary compatible. As the SimConnect is a simple C library (API) they should be - are they?