Regarding the comments about shmserver's safety, I wanted to point out that running the shmserver doesn't mean that you have to run multiple processes in it. You can still run multiple wine instances. The shmserver shows a performance improvement for a single application (granted special kinds of applications), not just for several.
The shmserver reminds me of how Windows NT and OS/2 handle 16-bit apps: they can each run in their own process, or can several can run in the same process to improve performance. I realize this comparison isn't exact, but I think the analogy is apt.
Why not include both servers? If, as Gavriel asserts, the changes to implement the shmserver can be small, maintaining both in the source tree shouldn't be horrendous.
--Juan