Although it is possible to switch the TCX to dumb cg3 mode and run X11R6 on that, Matt Landau of the X consortium said the following on the matter:
"But why would you want an accelerated 24-bit framebuffer to behave like a dumb 8-bit framebuffer under Solaris 2?
"OpenWindows versions 3.3 and 3.4 (bundled with Solaris 2.3 and Solaris 2.4 respectively) are perfectly reasonable R5-based implementations of X, with a perfectly good R5 server that also does DPS and takes advantage of the TCX. They have none of the brokenness associated with the old X11/NeWS server from OpenWindows versions 3.2 and before.
"Of course, if you want R6 libraries and apps, you can build R6 and run R6 applications against the OpenWindows 3.4 server, and still get full benefit of the TCX. Works just fine."