For Slate.js there's a PR to add Android support, looks like this is very hard to do well: https://github.com/ianstormtaylor/slate/issues/2062
If you are using React, Slate is IMO an excellent choice and the code quality/extensibility/community are great. I really appreciate DraftJS for coming out first and I contributed there as well, but Slate’s goals are overall better aligned to the needs of the community.
Draft appears to be essentially somewhat unmaintained, whereas the Slate community has continued to be very active (thanks for the Android support! That's one reason we ended up using Quill for now)
The built-in copy-paste handling is pretty messy to extend compared to Slate, where the system of normalizers works a lot better.