It's fun to see them hybridize, a few years back I grew standard green tomatillos, followed the next year by some purple and yellow varieties in the same spot. I haven't purposefully planted them since, but these multicolor volunteers keep coming back. This year I'm seeing two distinct growth patterns, with some staying low to the ground and others getting quite tall.
Tomatillos are obligate out-crossers. They always do better with some genetic diversity. Every few years you'll want to add in some plants from purchased seed or plants. This will help maintain the genetic diversity and avoid a bottleneck due to small plant numbers.
A long time ago I did watch a poor plant breeder decend into a little madness attempting the break the self-incompatability. Tens of thousands of failed pollinations before one mutant was fertile and produced seeds. Eventually she was able to produce inbted lines and make the first hybrid tomatillos variety.