What should you fix in 3.6.10?
Get rid of all those pointless FRED error messages like "Player ship has no secondaries". Have an option to disable all SCP error messages, as it's annoying to click through 10 error messages only to see that your mission runs fine. Get rid of all those Volition "quality control" features that are no longer needed. For example, you're not allowed to commit to a mission if "player ship has no weapons". This may have been useful to Volition playtesters, but at this point it's unnecessary.
In other words, it'd be helpful if FreeSpace didn't have so many error messages, or at least an option to disable the most common. Sounds like a lot to do, but as far as I can see it's just a matter of deleting extra pieces of code.