Biomediversity: I don't have a timetable, but I've been pondering adding new biomes. Swamps are on the list, as are more fantastic things like fungal forests.
Boats actually got a promotion on the schedule. They were originally pretty far down the list, but they've been promoted to 1.4.
Towers are rather stuck in their size, both to match the other fortifications and to make it possible to have the door "inside" the walls for every facing. I could see adding a smaller 2x2 watchtower structure though. A sort of introductory defensive structure.
Any feedback and ideas are welcome. I setup a public issue tracker (see here) which is kept up to date with plans and progress. A lot of the items are pretty bare bones, as I prefer paper for detailed notes. If I set the board up correctly, anyone with a Trello account (which are free) can comment on the cards.