I should warn you, I'm rating this in quite a selfish manner. For every potential theme I ask myself:

Will it be fun on every stage of the jam? Will I enjoy making my own project, reading about others' process, and rating all the games?

And only if the answer to all three is a definite YES do I give it a [+1].

So here is my justification:

Collapse [+1]: Old, but lots of definitions, so a lot of different games.

Rock, paper, scissors [+1]: Cool mechanic with a lot of potential.

Alchemy [-1]: Single definition, will result in lots of similar games.

Strange creatures [-1]: Seems like a lot of art, not a lot of gameplay.

Edge of the world [0]: There might be something here, I just haven’t found it yet.

Repair [0]: Again, only one definition, and although the palette is a bit bigger, still does not spark too many original ideas.

Build your own path [0]: Might be fun, might result in out-of-scope disaster and a lot of unfinished games.

Single resource [0]: Very broad, has a mechanical feel to it. Can be fun.

Momentum [-1]: Feels like physics thing, and that usually requires time, and tweaking, and downloadable builds.

Leave something behind [-1]: Can be fun, but is as old as a world, so I feel like I’ve already played that a million times.

Connected [0]: Same problem, a bit broader in terms of ideas, so scores an extra point.

Combinations [-1]: Seems like we’ll have a 1000 puzzles. Not ready for that rating.

Isolated [-1]: So broad it’s a bit of an overkill for me.

Stronger together [0]: Don’t mind it, but every time I see it, my brain starts playing ‘Happy together’, and I’m not ready for a full weekend of this.

Sanctuary [0]: It’s okay. If it doesn’t get too religious, then some problems may occur.

Folklore [-1]: Just let it go. It’s not happening. We tried, it didn’t pan out.

I might reflect on it a bit more later and change something, so if you want to correct me in the comments, I'd love to have a discussion.