I made one like that some years ago: it was interesting, but not without problems.
First: read up on air resonances. Bill Allen's article in American Lutherie #1, now out in the first 'Big Red Book', is a great place to start.
Moving the hole up toward the top edge drops the 'main air' resonant frequency a lot if you leave the size the same. Making the hole bigger, or using two holes for more total area, would raise it again.
There are a bunch of air resonances in the box. Some of them can be heard directly through the 'normal' hole, and some can't. Some of the ones that can't 'talk' to the outside air directly still influence the tone by the way they interact with the top. Moving the hole(s) to the upper corner(s) changes which air resonances are heard directly, and how the top works with the air. Since a lot of that stuff has been worked out by cut-and-try methods over many years to give a 'good' sound you're sort of on your own when you make such a major change. Not saying it can't work, but don't be surprised if you lose something you liked!
One problem on the one I made had to do with one of those normally 'silent' air modes: the one where the air sort of 'sloshes' back and forth across the upper bout. This happens at about 700 Hz on most guitars, iirc. The holes in the corners could 'listen' to that mode nicely, and feed sound from it into the room. The problem was that they were out of phase with each other. They're far enough apart so that they don't cancel out except right along the center line of the guitar just in front, but they do tend to 'beam' that pitch out toward the sides. When playing I'd have my head right in that 'beam', and any note that had any of that pitch in it would sound LOUD. So I'd play it soft. The folks out front didn't hear it the same way, and wondered why I was playing so unevenly. Little did they know.
Ah, the unexpected pitfalls of science....
BTW, regular Martin style X bracing does a pretty good job of extending the vibrating area up. The actual soundboard area that you lose with the hole is not all that much, and I didn't feel that the game was worth the candle. You might do better, particularly if you can get the fingerboard off the top.
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