Delivery :
There is always a lot of game using this (fedex quest etc), with drone, trucks etc..... it can be fun but i don't think is a good theme for new things.
Cartography :
I like explore.... but clearly its too large, and don't really need mechanics idea or too limited.
Shelter :
I think this theme is always in the final rounds..... but ....no, that can give a lot of good management and horror game, but already seen that.
Leave something behind :
Interesting.... item management, team management, choice...it can be good.
Parasite :
Parasite, virus....insect....no i don"t want that !!!! But that can inspire a lot.
The wrong tool for the job :
interesting too, can be funny, need reflexion !
Ascend :
Hum..why not .
Your health bar is more than just a health bar :
Playing with the "code" of video game can be funny, and that theme is interesting !
Salvage :
this theme is like delivery, but can be more various i think, can be good !
Strange machines :
Oriented puzzle/reflexion, but also construction, recolt piece to make your own machine etc...... really good and large, but not game mechanics oriented.
Signal :
Bipbip biiipppppp, many interpretation....can give really original and complex game, or just narrative with alien.
Limited visibility :
Remind me cartography, but can be used for horror game, ineteresting too.
It spreads :
Contagion, virus,parasite......not fan, but can give interesting mechanics and stressfull gameplay.
Clear a path :
why not remind me a lot of escort game.
Every input does two things :
That can be ridiculous, but than may give you a choice at each second, very interesting.
Start small :
Not a theme, an advice for the ludum dare i think !