As I understand it, the main difficulty with building old Knossos is that it uses so many different technologies. This will be improved in new-Knossos, but as you noticed it won't be ready any time soon - it depends on ngld who has not been available recently. A couple of other people are working on their own mod managers, but again these are in the very early stages of development. There is also the old FSO Installer, which still works and is still maintained, but most mod makers do not deploy updates for that platform.
Regarding the mods on Knossos - as far as I can see, most of the mod descriptions do a pretty good job of indicating whether the mod is finished or not, and if any future releases are planned. And very few publicly available mods are actively undergoing beta testing. This doesn't mean they are free of bugs, though. Are there any in particular you noticed?
Mid-mission saves was covered fairly well in the other thread
- essentially, this is up to the mission designer; there is no mid-mission save built into the engine. However, as mentioned, most missions are short enough to mitigate this problem. Be glad you aren't playing the infamous 40-minute missions from X-Wing, TIE Fighter, or Wing Commander.