The first question I would have before becoming invested in something like this is, what type of mouse: gaming or regular use or a hybrid between the two or one of each?
I would love to have it be USB-C, bluetooth and with an option to attach a cable for those who like their mouse devices wired for gaming and other things … Very similar to how a console controller works. Wired and wireless charging, especially for those who have a mouse pad that offers wireless charging.
I look for comfort, precision and reliability. It needs to be light, ergonomic, and fit larger hands. I find it frustrating how it seems most mice are fit for small hands as if young teenagers are the only ones buying them. So maybe have a few different sizes or the ability to adjust the size of the mouse from the back so that it can conform to and appeal to a lot more people.
The button amounts will differ between people based on the intended usage but I would love it if the buttons were re-mappable with an option to turn an un-used button off. Have the ability to change the amount of pressure needed to push on a certain button to avoid accidental mouse clicks.
Like most people looking at this, the more responsive the better. It should work on most surfaces or have the ability to program the mouse to recognize a certain surface for better precision needs, like the same way you would possibly re-map the buttons or an already programmed button for several surfaces right next to the DPI button.
A cool feature, besides the ones mentioned above it is to have a heating and cooling option to cover the summers and winters. I would be up to having different textured skins, different button options and a variety of colors. A memory button to remember certain settings, like using a finger print to sign in on a computer or phone but on a mouse.
If you are going to develop a mouse, you may as well develop a keyboard either at the same time or after. The Eve package sounds amazing as long is it remains premium.