As a new user, and not as an experienced programmer, since this is supposed to be a hobby and a source of entertainment for me, I think that stopping from evolving is bad, I recently started reading more and more docs for .net 4, and forcing .net 2 is a bad idea (but, again, isn't SVN supposed to be used mainly by who knows what is doing? so, where are those noobs?).
Nonethless, speaking of me, our shard begun migrating from an old emu to runuo 1.0 or whatever it was (but this migration failed, there was no source of the core at the time, developers of the time stopped developing it too because of this..we were in need of it at the time, our old emu was too buggy), then to runuo 2.0rc2, but for about 3 years we suffered for the way it was, many many things has been changed, and almost anything is different now, but we updated core to recent changes, updated to support new clients, and used most of the things that .net4 can offer, me too, as an unexperienced programmer, as I said above, have begun reading and I've taken an advantage from the new core. We have also maintained the network code and debugged it, I think I've sent a patch to Asayre (that contains writing errors), we are still using it with many days of uptime without any crash/deadlock...but, anyway, there I am nobody, and for sure our shard is really different from osi/yours I think, I don't think there's still something left of the old code in scripts, said this, again, retaining .net 2 is a BAD idea IMHO, you're blocking active development from who is trying to learn the language, and who begins reading runuo code and finds it still uses old framework, will try other roads, finding skilled people that want to program for an old game like uo isn't easy, and when someone that couldn't loose too much time starts to see that this isn't something one wants before catching the notch and beginning to get amused...too bad, he/she will go away...
I think all of this could be done in reverse mode, make .net4 mandatory and .net2 optional, who want the old piece of software for sometime can still use it, but I think that .net2 is dead on an emu like this.
I hope at least that what I wrote is clear enough.