At a glance, it looks like Sui Generis isn't dead. It's just on hold for longer than they initially implied. They're using Exanima as the vehicle for completing the game engine, and will resume work on Sui Generis when that engine is done. And they are still very much working at it. I picked up Exanima when it was first released 5 years ago. It has been massively expanded since then, and there are still fairly frequent updates. I've returned to it 3 times over the years, as in it temporarily became the main game I was playing for a month or two, and it felt fresh every time. They're claiming to be finished tweaking core stuff like fine-tuning the physics and controls of movement and combat, and are adding the last major gameplay features on top of that -- ranged combat, magic, and multiplayer, which they claim to be getting easier and easier to work on as they establish better foundation. And when those are finished, they're going to consider it done and return to Sui Generis.
Exanima is more difficult than most games to get into. It takes at least a couple hours to begin to get comfortable with the controls. But once you do, it's incredibly rewarding. It has the most fluid and dynamic melee combat of any game I've ever played. There is a rhythm and flow to it, and once you get zoned in with it, your fighting can look pretty badass instead of drunken stumbling. And there's a greater satisfaction, I think, that comes from mastering an adaptable intuition to a dynamic flow, as compared to your typical game that involves rote repetition of button combinations in response to rote repetition of enemy behavior patterns. Baiting your opponent into an awkward swing so that you can step in behind it and fell them in one solid blow to the head with superior balance and timing just feels amazing.
My only criticism of the game would be the dev's attitude towards save games and hardcore difficulty. I'm a pretty decent gamer, and I've never beaten it. The levels are incredibly difficult to navigate and there's no mapping system. It gets frustrating running through the same areas over and over again on repeated attempts and never seeming to be able to figure out where you're going no matter how many repeated explorations you do. Arena mode is currently the most fun, and it is quite fun.