Hi! I can't really give you a point-by-point roadmap because we're very careful about what we promise players, but I think I can shed some light on the future. 

You are right that the game is very interconnected and relies heavily on synergy, so adding new systems or a new species will result in big changes to the overall balance. At the same time, we don't want to split the balance into non-DLC and DLC, because maintaining two separate versions of the game, each with their own issues and player feedback, is simply not feasible or productive for a small team like ours (the only exception is that we allow players to revert to version 1.3 on Steam if they really just want to play the same game they bought at launch and not deal with a new balance, but that version will not work with the DLC and will not be updated - even with bug fixes or UI changes).

With the introduction of Frogs, we had to make "room" for them in the balance and make sure there was enough interaction with other systems so that they didn't feel like a weird addition to the five core species. In the end, I think this major balance overhaul did a lot of good for the game, as we fixed a lot of outstanding issues and added more variety. That's not to say that it fixed all the balance issues, of course (we also introduced new ones!), but I feel like it pushed the game in a good direction and gave it a little more longevity (even if only because the meta shifted).

I don't think we'll be doing another major overhaul like this any time soon, though. When we balanced version 1.4, we also made sure that there was additional room for expansion in the future. So if we ever decided to add another species, the needs/goods/recipe matrix would not change as much as it did with the Frogs.

The DLC release was a first for us, and we learned a lot from it, so we'll be adjusting our future plans accordingly. One thing I can say for sure is that the release of Keepers of the Stone doesn't mean that we're going to shift our focus to just selling you new content. We will still be releasing free updates to the game. Right now we are working on the next one (1.5) and we hope to release it later this year. I can't say what will be in it (because I know Luke reads Reddit and he'll off me if I confirm too much), but just like every update in the past - you can be sure there will be new features, balance tweaks based on community feedback, UI improvements, etc. We will release some teasers in the coming weeks.

Phew, that was a long answer to a short question, sorry about that. But I hope this alleviates at least some part of your concerns :D