I have installed the macOS 10.15 "Catalina" developer beta, and unfortunately it brings bad news.
What makes up the Mac client able to run City of Heroes is a fairly old open-source project called Wine. While the project is still updated with new or patched modules from time to time, the Wine application itself has basically been abandonware since 2016. It's a 32-bit command-line application that has been hacked to be able to load 64-bit modules to then launch either 32-bit or 64-bit Windows apps. What that means, simply, is it's like hacking Windows XP to run *some* 64-bit software. Badly.
Unfortunately, macOS 10.15 no longer will run 32-bit command-line applications. And very soon, Debian Linux is rumored to be joining it (which means Ubuntu will follow as well). It means macOS will no longer be able to run City of Heroes, even if the developers somehow make the game itself 64-bit capable - because the part that makes it run, Wine, will never be fully 64-bit.
So the current plan is, as of the final release of macOS 10.15, the Mac client will have to be discontinued, and the Mac version of Island Rum will have to be discontinued as well.
The plan is to not get focused on trying to freeze Mac players in time to where they have to find a way to keep their OS at 10.14 or below in order to play. Instead, I would rather move on, focus on figuring out a reliable virtual machine product to use instead. The current choices are Parallels, VMWare, or Virtualbox. I'm going to test each of them in macOS 10.15, and find out which one has the best balance of performance and stability. A small bonus to that will be that the testing will also likely improve the play of other Windows games as well. My tests should be complete long before the macOS 10.15 final release.
Since macOS 10.15 is still a *very* early beta, there is always the possibility another product might come along to take the place of Wine, or that Apple itself will come up with some solution, or that some other group will take up the Wine project and finally update it properly to 64 bit. I can't depend on that happening in a timely fashion, however, so my current plan will have to eliminate that possibility for the time being.