Split OSK keyboard layout when wide enough
For handheld use, it makes sense to (at least optionally) put the extra/unused horizontal space in the OSK in the middle of a split layout, instead of on the left and right.
This makes the keyboard usable in two-handed landscape use for thumb typing, where now it can only be used very awkwardly by gripping a landscape tablet/convertible on one side and supporting its entire weight in one hand while typing with the other - both unstable/risky from a grip perspective, and slow from a "single finger hunt and peck" perspective vs. two-thumb typing.
So basically, something very similar to the Windows OSK listed under relevant art on https://wiki.gnome.org/Design/OS/ScreenKeyboard (or the iPad split keyboard).
It could use similar "tear apart"/"push together" gestures to split/join, although that could be added at a later date with an interim "use split mode in landscape" in e.g. Settings to simplify implementation.