tl;dr: Plug-in developers can now update their plug-ins to run in 64 bit mode.
There’s an undocumented change to how the Web Publishing Engine runs that affects where to install plug-ins to be run by CWP.

A few weeks ago FMI released the FMS 12 v2 update, adding support for 64 bit plugins used by CWP solutions. FMI also released a new software developer’s kit (SDK) for plug-in developers. Until this SDK, there was no way for plug-in devs to update their plug-ins to run in 64 bit mode. So some FMS 12 plug-ins (possibly, all, I’m not sure) could, until this update, only work in 32-bit mode. Which was okay for most purposes, but the Web Publishing Engine (WPE) runs in 64 bit (on a machine running in 64 bit mode…you could run your 64 bit machine in 32 bit mode).

So far, I haven’t seen any release of an updated plug-ins but I’ve read or communicated with several devs who are actively working on updates: Goya, Troi, 360Works, and 24U. I’m assuming most of the top-level plug-in devs are on the ball.

There is one poorly documented change that should be noted. It’s documented a pdf in the new plug-in SDK and nowhere else that I can see.

There is now a new folderpath to install plugins to be use by Custom Web Publishing (CWP). Instant Web Publishing (IWP) is the same filepath as before (/publishingengine/wpc/Plugins), but CWP plugins now go into (…/publishingengine/cwpc/Plugins).

This change is not reflected in an updated FMS document (otherwise a superb pdf). It’s in a pdf that comes with the plug-in SDK. When called by CWP, the function Get ( FileMakerPath ) also returns a /cwpc/ path.

Thanks to Nick Orr at Goya and Diana Budding at Troi for being patient with my questions and to Obinna Oparah at 360Works for a couple informative posts on FM Forums.