I don't like hybrids with any species. Not with birds, not with fish, not with mammals, and not with reptiles. No thank you.
Specifically with tortoises, there are many diseases that are very difficult to detect and diagnose. Even if a positive diagnosis can be made, sometimes, there is no cure. Species should never be mixed. Even if we ignore the disease risk, species should not be mixed for behavioral reasons. Like mixing African cichlids from Malawi with South American angel fish. Its not going to end well.
Humans have been making hybrids of all kinds. Plants, live stock, and yes pets. I agree with keeping species pure, but on the other hand imagine more colorful tortoises that could be more cold Hardy. Like a star with a marginated or Russian. More cold Hardy and robust but yet more color. Eventually they'll be able to genetically create them in a lab with choose of size, color, and hardiness. Lol jk. I only replied because I live in the Northeast and to have a tortoise that could live outdoors year round would be great.