This past week, I received a flurry of emails from software vendors, advising Mac users to hold off updating to macOS Catalina, because it won't support 32-bit binaries at all.
Most significantly, one of these emails came from CodeWeavers, makers of CrossOver, an excellent commercial implementation of WINE--the same technology which powers NetVSTHost for Mac. They included a link to their own blog post which explains why this issue is so thorny.
The heart of it is this:
Most Windows applications our users run with CrossOver are 32-bit and CrossOver uses a 32-bit Mac executable, system frameworks, and libraries to run them. This will break with Catalina.
So, even if I were to repackage NetVSTHost for Mac using the most recent 64-bit version of WineBottler, the resulting 64-bit binary would run under Catalina, but would only be able to run 64-bit Windows VSTs. In my view, this undermines the most important use-case for NetVSTHost for Mac, so I see little point in pursuing it.
NetVSTHost for Mac was never much more than a convenient little hack--a way to run the 32-bit, Windows-based NetVSTHost.exe program on a Mac, without having to set up a full virtual machine (using e.g. VMWare Fusion, Parallels Desktop, or the Mac version of VirtualBox), or better yet, use an actual Windows PC.
I would advise anyone who has come to rely on NetVSTHost for Mac, and who anticipates upgrading to macOS Catalina at any time, to look into the two-system approach for which the NetVST Project was originally conceived. Details can be found on the NetVST Project wiki.