1.2.2 does away with the runtime's infamous genericResetcalls, instead much faster code is produced.
The SSL bugs have been fixed. At least that's what I have been told.
There is a new warning about "Observable Stores". I have yet to see a case where this warning indicates a real problem and so your config should probably disable it. Code to do that is:
# nim.cfg
@if nimHasWarningObservableStores:
warning[ObservableStores]: off
@end
Apart from that 1.2.2 focus was ARC-related bugfixes.
Yes we still do, the implementation is currently integrated with net.Socket. You can open an issue on GitHub requesting a pluggable mechanism and I might look into it. It's not really that hard to replace the current system with a pluggable one, but there aren't enough interest to go for it atm.