Space above the space bar.
Realizing that screen real estate is precious, it would be nice to have the bottom row a bit separated since I hit space and the period accidentally quite often. Even if the top few pixel rows of the bottom row were "dead" it would help.
Bryan Block commented
This is currently my biggest frustration with SwiftKey - I type very fast and am constantly hitting the space bar instead of bottom-row keys. I've tried using all three keyboard sizes and it doesn't help. Other than slowing down (and isn't this keyboard supposed to speed things up?), I don't know how to re-train myself. None of the space bar options help - they either put in a space or auto-correct the word, which if I don't notice, results in the last half of the word being duplicated. I can't even count how many times I've had to fix "Thanks ks" since I hit the space when going for 'n'. THIS IS SO FRUSTRATING for a fast typer. If the rest of the app wasn't so good I would have switched away already.
This would also help to avoid accidental space and punction word terminations.
David Neto commented
Either that or spacebar hits on the top could try and keep guessing a word with a letter from the vicinity instead of starting from scratch.