Would be nice if we could split properly for hotbars, don't think we need it for within the creative inventory itself.
Throwing a warning when trying to split "Can't split items in creative mode" should be good enough for now though, unless you want to implement the stuff mentioned above.
What works:
- Single item splitting for your hotbar
What doesn't work:
- Single item splitting within the creative inventory --> I think that's OK
- "Split all" for your hotbar
- "Split all" for your creative inventory --> I think that's OK