For the existing reflection implementation for port forwards, I don't really know for sure what is breaking it for UDP.
You could test the 1:1 NAT reflection to see if that works, as it is possible to implement the same rules for port forwards. For this test, on System: Advanced: Firewall/NAT, enable "Automatically create outbound NAT rules which assist inbound NAT rules that direct traffic back out to the same subnet it originated from." (that really needs a shorter descriptive name to the left...). Create a 1:1 NAT rule on LAN with some IP address for external IP other than your WAN IP or one on your LAN (it can be anything for this test, even just some made up IP, as long as it isn't one of those). You could do a rule for testing your whole LAN or just one IP, just whatever you want to for the test. Try locally accessing your UDP services through the appropriate "external IP" for the server you want to test (depending on how you configured the 1:1 rule) and report back on the results. The 1:1 NAT reflection code can be used for port forwards as well, but the code for using it as such is not there yet. If the test succeeds, that implementation would work for your UDP port forwards if/when completed.
If you want to pay something to get this done, whatever you think would be fair (fair to you or to me) would be fine with me. I'll probably finish it sometime anyway, but I might be more willing to do it sooner rather than later if someone was going to pay something for it, and I'd be more willing to do the work to make a package to retrofit it onto 2.0.1.