We are currently shipping Xorg Xserver 1.5.3 and Mesa 7.2, with a bunch of patches. It would be much better if we could upgrade to modern versions. This makes development easier and gives us bug fixes and enhancements. The rest of the TigerVNC user base and developers are also not interested in support for this old server versions.
Another issue is security. According to http://www.x.org/wiki/Development/Security, 1.5.3 should be fine, but new security issues can pop up at any time, and if we are using an old version, it might be difficult to apply the fixes.
See also bug 2770.
Apparently upstream is now converging on the xfree86 portion of the Xorg tree. Xvfb (on which Xvnc is based) is getting thrown out in favour of Xorg with a dummy driver. We should probably look at following this model if we want to reduce our maintenance burden.
This got done as bug 4417. Marking as duplicate (although wrong way).
*** This bug has been marked as a duplicate of bug 4417 ***