Just make sure you don't beat yourself up over this too much ok? It is very normal for games to slip, and even though you are in this vanguard of the 'new' crowdfunding era of independent game dev, you are still an indie dev with no hard nosed business people (and lawyers) breathing down your neck for returns on their investment.
It's just you and us, and for my part take as long as you need to make your perfect game (i know others will not be as patient, but you have a spread of feelings on this from all your backers). A few points on this from that last video:
1. LT still needs this time, you will want to make those improvements you will need too, the new ports on planet needs fleshing out a bit etc.
2. Adding the mod support will give you an option to not have to finish it as 'fully' as you may wish (in a perfectionist method), which is a good thing. As you say it will be amazing to see what modders can do with this, Morrowind is a case in point.
3. Those that have the beta access can have more time to help you finish this project up, that is good too.
So overall, i think you just made the right choice and gave yourself more time to make your game better, certainly good enough to keep us all happy. Keep it up, your doing magic