You can also make kefir from plant milk, such as almond, oat, coconut or soy milk. The results can vary, so it's best to find out for yourself which ingredients taste best.
Anyway, many vegans swear by coconut milk kefir, made with canned coconut milk with a high fat content. This makes a very rich, creamy kefir.
Mixing different types of milk is also possible, of course, and a mixture of goat's milk and coconut milk is a very popular variant among milk kefir professionals. So the possibilities are endless, but sometimes the kefir tubers need animal milk, in which they again get all the nutrients they need.
We have had good experiences with adding the tubers back to animal milk at least every 2-3 rounds. Probably the smartest solution is to always keep a small jar of kefir tubers in cow's milk in the fridge as a reserve.