I would be really nice, is it already in plans or no one thought about this?
I think the issue with this is that there is no language compartmentalization in those modes. A mass review button would jumble up the languages in a not-so-pleasant way. For example, if you are learning both French and Chinese, you would need to switch between the Chinese and French keyboards randomly throughout your learning sessions. Or, if you are learning two languages that use the exact same writing system, it would be oftentimes be difficult to know which language is being asked for.
There are, of course, ways that I can see around this. Just one of them is the possibility that they might add one review button for each language. But further thought tells me that that’s not much better than simply filtering your courses using the method they have now.