As part of a project I'm working on I fixed a bunch of ARM/modern-Linux incompatibilities in the old XFree86 X server, so that
now I have a version that runs on the Raspberry Pi. This includes the Tiny X framebuffer server Xfbdev, which currently isn't available on PiCore. Looking through the forum it seems that Tiny Core's stripped down version of Xorg's Xfbdev was tested on PiCore during initial development, but found to be unstable and therefore scrapped. I've tested my XFree86 Xfbdev on a Pi Zero and a Pi Zero 2 and not experienced any crashes, although the mouse acceleration needed some fiddling and still seems a little laggy (might just be to do with the wireless mouse I'm using).
I've tested a few programs, including Firefox running from a PC in a remote window (PiCore's firefox.tcz seg. faults for me on the Pi Zero 2 regardless of the X server used). Also Dillo, "Links -g", aterm, xeyes, twm. It seems stable. I've only tested on the composite video output so far though.
The current extension that I've got, which needs some minor modification to account for font paths, is 500KB, so that compares well with the xorg-server.tcz extension which is 2.63MB and depends on mesa.tcz which is 2.85MB. It's bigger than Tiny Core's Xfbdev extensions on x86 (340KB) and x86_64 (356KB) though, but has all the original Tiny X features like TCP support.
Anyway I thought it might be useful for people looking to start X faster on a Raspberry Pi. On the other hand it's not using Tiny Core's Tiny X codebase, so maybe that's too confusing (could name it something like xf86-Xfbdev.tcz though). Also the configuration might not work as well as on PC because PiCore seems to assume that Xorg is the only server available (jwm.tcz depends on Xorg.tcz, for example). It also lacks the Raspberry Pi optimised framebuffer driver that the Xorg server uses.
Basically, if there's interest then when I have time I can try to build a good extension for it. Or if it's not wanted because it'll cause confusion or something, then I won't. So let me know.