Remember also that I am using kubuntu (KDE desktop), though with the "low-fat" settings (which seem to help a lot). I am experimenting with kubuntu again because the missing-menu-bar syndrome of the Ubuntu Unity desktop they are forcing on everybody (much like Microsoft attempted to force Vista on everybody), can be very confusing to users, and I want this to be easy to use.
I think 12.04 may be soon enough for my music education initiative, since I want it to go out with a long-term release, though in the past I have been burned by lack of reliability of the ".04" releases. The ".10" releases have been better in the past.
Remember that not all of the .04 releases are supposed to be reliable long-term support -- only those released on even-numbered years. The <odd>.04 releases are often the least stable in a two-year period (and certainly that was true for 11.04, which replaced the entire top level UI). So if you want stability, stick to the LTS releases.
I suggest that the real reason to get the fix out there, is that Fluidsynth will sound worse, and people won't know why. They may never have tried it before, and just assume it to be a mere toy, going on to something else. Not having the fix can give Fluidsynth a bad reputation, which really should be avoided.
That's only true if this bug is widespread. To date, it seems like you are the only person with this issue. That's not to say it isn't important -- just that it probably wouldn't be as disastrous as you say.
We should be careful to distinguish the inclusion of this fix in Ubuntu 11.10 versus inclusion in Ubuntu 12.04. It is highly likely that the fix will be included in 12.04 (as long as David releases 1.1.5 some time in the next few months) -- you don't need to do any special petition or anything.
It is highly unlikely that the fix will be included in 11.10. The Ubuntu maintainers are very strict about what updates get released after the launch of a particular version (read the link David sent yesterday). Unless there is a security vulnerability (which this is not), loss of user data (which this is not), or a package being completely unusable, then they are unlikely to comply with your request. You might argue that FluidSynth is completely unusable for you, but it sounds like it is only a problem in certain configurations (as you described in detail). Other users may be using FluidSynth fine, and the Ubuntu maintainers will want to respect that and not force an update which could have unexpected consequences.
So (again, while you are welcome to try), it is probably best to just not bother with the 11.10 release. It will naturally appear in the 12.04 release, and in the meantime, you may personally work around it by using David's PPA.
Just my opinion.