Which is, in a nutshell, why it's important for a formal language to be easy to read and write, and why eliminating overly verbose notation matters. It's not just for computers...
In this respect I think AsciiMath doesn't go far enough, precisely because of the Ascii part. Especially for super- and subscripts, why not use the corresponding Unicode characters?
At least on my keyboard, "x^2" is one keystroke more than "x²", and the latter is much more redable.
AsciiMath optimises for ease of use in both reading and writing. Fewer people know how to write x² than x^2, yet virtually everyone will read them equivalently. That's not true for n/2 versus \frac{n}{2}.
On my Linux Mint 18 KDE system, ² can be typeset by typing AltGr-2 (I can get ½ by pressing AltGr-5). I am using an Italian keyboard, but I bet this works with US keyboards as well.
Recently I used Windows 10 quite a bit, and the number of AltGr combinations available on Linux has been the thing I missed the most!
Every german keyboard can do this. And a quick (non-exhaustive) google image search shows that many other keyboard layouts support it, e.g. french, turkish and portuguese (brazil but not portugal)
If you want email to have autocomplete, then it does. 'Email' isn't a client. The client you choose to use is. Write your emails in vim -> now you have autocomplete.
No. The way to write your emails in vim is to use an email client that lets you open the text in an editor of your choice. E.g. mutt, or a webclient combined with an add on that let's your open textarea in an external editor (vimperator or its all text).
P.s. emacs sounds like a great OS - are there any add ons that allow one to open its textareas in a decent editor? :p