Ok, I know I'm not going to make any friends saying this, but I would take that shot in a heartbeat depending on a good amount of variables, such as the elevation angle (ground to treestand height). I would wait the deer out as long as I could to get a better shot of course, such as a broadside or quartering away, but if it didn't present itself and I knew the gig would be up in seconds, I'm sorry, but I'm taking that shot. With the speeds of today's bow, mine included, I would have no issue with it. I think every situation is different in that the size or desperation factor would come into play when a hunter questions this shot. Such as, if it was a p&y or booner and it was the only shot that presented itself and it was close to the end of the archery season, it would be a no doubter for me. However, if it was a doe or just another average buck, I think I would pass just because your chances of success are dimished slightly. I still like the shot though, even though the brisket is a tough unit I believe this shot can be made with success of hitting vitals and is a good look at the heart. LIke I said distance, elevation, shot presentation, calibur of deer, time of season all play a role, but I've made this shot and have had success with it. Granted, only on two deer in my life, but they were short tracks nonetheless. You can still miss vitals however, with a glancing blow off the brisket (very tough part of the animal in terms of bone and cartlidge), or between lungs and beneath the heart. These are all very possible with the shot, however, that is why some of the factors above are taken into account I believe. It's all dependent. I know most bowhunters would severely frown upon this shot, but I say it's possible with good shot placement, understanding of the vitals locations, proper impact force, a good broadhead, enough penetration (momentum), and being aware of the angles.
My biggest fear, however, is what you stated above. Not having an exit hole. Only blood from an entry hole, which more often then not is above the wound channel. So blood will pool inside for a great deal of time before spewing out. That is where elevation can hurt and/or help. You risk a glancing blow off the brisket with treestand elevation, but with ground swatting it you risk no exit hole. When I have taken those two deer in this fashion, I've never aimed dead center of chest, as that would be bowhunting suicide IMO. If that gets those aroused on this site I don't know what will, except that I saw my father once shoot a doe in the neck center white patch at 15 yards and she dropped like a sack of potatoes and never got up. As you can see I think about this shot a good deal of time. Doubt it helps you, but that's how I feel on the subject.
"I enjoy and become completely immersed in the challenge and the increased opportunity to become for a time a part of nature. Deer hunting is a classical exercise in freedom. It�s a return to fundamentals that I distinctly feel are basic and right"-F.B.