I explored floppy bean bag like cells, but I had these problems:
1. Most systems like this aren't really that robust. You can have the cell collapse in on itself in a tightly coupled mass of vibrating goo. Basically game over the cell. Which is fine for a game where you only lose a life and start the game over, but for an evo sim it's a disaster.
2. Floppy shapes are not always convex, making collision detection significantly more difficult. We'd probably never get sims with more than a few hundred bots run at any decent speed.
3. I have no idea how a bot would control its shape from the DNA. Actual cells use a sort of fuzzy logic, pulling various bits of its cytoskeleton with varying strength, which results in the final shape. I don't really have a good idea of how to accomplish something similar with the way DNA works in the program.
Still, if those three issues ever get solved, I'd really like to explore floppy ameoba cells. It's just beyond my capabilites (and most others' capabilities from the looks of it).