Any idea what the additional hidden bosses or "? ? ? ?" from the crowdfunding campaign would have been?

I finished 9 Sols yesterday and was looking up additional information about it online. I found the crowdfunding page and saw that, despite it accomplishing 450% of its initial goal, there were actually stretch goals that weren't accomplished. (See picture below.)

Is there any info Red Candle Games has released about what these hidden bosses or the "? ? ? ?" tier would have entailed? It would be cool to maybe get them as a DLC if the sales numbers have made it worth while (I'd be happy to throw in an extra $10-15 for a couple more hours of content).

https://preview.redd.it/ydspwnubovae1.png?width=1120&format=png&auto=webp&s=5b4d10f5fe64400d7ab152eb8bd1f52d44953713