Yup.
Sui Generis is being worked on simultaneously. Anything developed for Exanima is used in Sui Generis.

It’s one of my favourite games despite not being finished yet, but it will probably gain more popularity once we get co-op and a multiplayer arena mode.

The performance issues are only inevitable with this engine. There’s a limit to how much refactoring and “adding features” you can do. At some point you just have to start from scratch or switch to a better available solution.
Even if they could’ve done a better job “optimizing” the game, they’ll always be limited by this engine.

Although to be fair, most games and game engines today aren’t as focused on performance like they used to be.
I can’t think of any modern game engine that uses Assembly in any meaningful way, other than Exanima’s engine.
Also evident by how frequently GPU companies end up fixing and improving game performance for specific games with their drivers.

Thrive

tl;dr: a better Spore

From the site:

Thrive is a free, open-source game about the evolution of life.

From the lowly tidepools of your home planet, you will rise to cosmic dominance. At every step, powerful creation tools and deep simulation mechanics will aid your species’ development. Revolutionary Games is the open-source team of dedicated volunteers aiming to make Thrive a reality.

Our team seeks to accomplish two major goals: create engaging, compelling gameplay that respects our players’ intelligence, and remain as accurate as possible in our depiction of known scientific theory without compromising the former.