With your other wishlist item, to turn manually on on the surface, what do you mean? Start the dive prior to when the sensor would? What is the advantage?
My desire is for a manual off or sleep. Like you I've had my Eon's stay on and fully drain the battery, either over night or if put in a cool box with damp gloves in a hot car. It's a peculiarity certainly in the Middle East, where humidity can keep the sensor on. I't often exasperated by minute salt residue on the sensor becoming damp which is enough to keep the computer on
The solution is to clean the water sensor regularly (I do once a month) with a little tooth paste on a brush, and then post dive give it a fresh water rinse, blow the water out that sits between the sensor and case, and dry it. It sound more complex than it it. but a manual button press to turn it off would be great. OR a simple time out, it its in Surface interval for say more than 15 mins
I always press a button on my computers before I dive to confirm they are on, but otherwise like others the pressure sensor signal at 1.2m/4' is good enough.