Sorry for the delay responding, but that was a lot of suggestions at once, and this week has been even more busy for me than usual.
I don't think it should be too difficult to add an AMM between Hive/HBD if it looks like it will help liquidity. But before our team built one, I'd need to review how these things are performing in the real world, I've mostly stayed away from them because I felt many AMMs are marketed with an overly rosy view.
30 day window could be possible, but I don't know what the performance tradeoffs would be yet.
Expanding consensus to 29+2 has one known disadvantage: it increases the time to transaction finality. It's not a huge increase though. Overall, I don't have a strong opinion on this issue as I haven't seen any real problems coming from the current number of witnesses. As far as the other changes go, I'm not eager to tinker with rewards ratios, as such changes are always controversial.
How much longer do you think the code will require this level of development?
It's hard to say. As far as hived goes, we've done many of the things I would characterize as critical to scalability of the chain. But there are still several important improvements I would like to make. My guess is we can complete them in the next 6 months.