Have you written to Zoom to request this? They seem pretty good at adding stuff the users want (H4 to H4n added quite a lot that I had talked to them about), and it sure couldn't hurt to contact them.

Mind you, as little power as they draw, leaving mine on is little hassle, and powering it down manually gives me more confidence it won't do it when I DON'T want it to happen!

Sort of like my computer. Normal use, yes, I set it to sleep after 15 mins. or so, but when I'm booted into my OS for making music, sleep is ALWAYS set to 'Never'...