I wanted to create a similar thread myself.
My plan for this 7DRL is to create a more complete game based on
Hyperbolic Rogue. The current version has been featured in several media, to my great surprise, as this was just an experiment, more a concept than a real game. Since the concept of using hyperbolic geometry makes an extremely minimalistic game so popular, I expect that merging it with a more complete game could bear great results.
I plan to keep the general (a bit minimalistic and DROD-like) style of gameplay, though. I feel that the usual mechanics of stats, hitpoints, heal-by-rest, accuracy and dodging, armor, and so on are overused, boring, and don't bring much to the game. Hydra Slayer's mechanics are more interesting and would fit the hyperbolic world, but I don't want to repeat it either. Especially 7DRLs should try to replace this with a more interesting, tactical gameplay.
The new version is planned to allow players to explore several types of lands, each of them including specific monsters, terrain features, mechanics, items, and treasures. One of these lands will be the icy one from the current version (although with new items and boundaries with other terrains), so Hyperbolic Rogue will be a kind of a subset of Hyperbolic Rogue II. I am afraid that this might be considered cheating by someone, but I don't think this is a problem (the original Hyperbolic Rogue was an out-of-challenge 7DRL itself, and e.g. Jeff Lait also tends to reuse parts of his previous 7DRL entries, and also this is roughly equivalent to reusing "@ moving on screen", with a difference that the geometry is very special).
My other plan (and a suggestion to all 7DRLers) was to see what is the theme of the
Experimental Gameplay Project and try to make the game consistent with their theme. Since this project also aims at creating experimental games in 7 days, I think it is a very cool idea to make the game which fits both challenges. (Februrary's theme was
Infinite World, which fits Hyperbolic Rogue extremely well.) March's theme turns out to be
Economy. I think this theme also fits roguelikes quite well, since resource management is so important. I'll try to make the 'economy' in HyperRogue II interesting. I also recommend everyone to try to create a roguelike with some kind of interesting resource management, and swamp the Experimental Gameplay Project with roguelikes.