it is unlikely that QWERTY is optimal for this use case
    since it certainly was never designed for this

QWERTY was designed to minimize jams on manual typewriters. You get a jam when you press two nearby keys in quick succession. This is actually extremely similar to the layout constraint swype operates under.

I was talking about Minuum, not Swype there. For Minuum, "maximizing alternation" is not a priori obviously the same as "maximizing the information theory distinction" between two subsequent keypresses. In fact, the fact that you are trying to maximize separation tends to imply that you are thereby tending to make the next keystroke more predictable than it should be, which is to say that the likely next keystrokes have clumps where too many of the most likely "next letters" are all on one side, which is suboptimal from the information theory perspective. QWERTY is not likely to be optimal for this use case; it may even turn out that the optimal keyboard resembles it as little as QWERTY resembles Dvorak.