I'm by no means an expert but I wanted to comment on these three points.
First, ventilation is through the front only, both in and out. However, the top should be accessible to your hand to adjust lens shift, zoom, and focus. There are no vents anywhere but the front.
The lens shift on this is definitely great. I read that it automatically compensates for the minimal keystoning that is unavoidable with lens shift. I couldn't see it and I'm using about a third of the full range of vertical shift. There is also a chart I saw somewhere online (sorry, can't find it) that shows lumen loss at maximum shift. I want to say it was something like 12% but that's off the top of my head and might be totally wrong. Search around, you can probably dig it up. Here again, I'm using about a third of the v-shift range and I'm amazed at how bright this thing is.
As for waiting, I think I read that Epson was one of the only companies to roll out a major update last year
-- my guess is they'd sit back and ride this one out while everybody else plays catch-up.
On my last PJ, I kept waiting and waiting for The Next Big Thing -- there will always be a Next Big Thing. The 5030UB is pretty awesome -- buy it and enjoy it, I say.