No, please don't, here is one voice against "let's do it totally different for idiots". Next you want to have 3 confirmation dialogs "do you really want to send" followed by "did you prove-read your mail again?" followed by "you clicked YES too fast, go back to start and prove-read again".
Also, worst thing you actually can do is to put the save/send/ok button on the bottom when all other UI elements are on the top of the UI (which is usually the case in mail clients).
I don't think slippery-slope is an appropriate argument to make here, or really anywhere.
To answer the UI elements on the bottom, I'm not sure I actually press the Send button at all, instead opting for a keystroke depending on the client. The physical analogue I base my request off is the order I fill out a letter or card--I write my message, then I sign it, and then I seal and address the envelope.
Beside that, what's to keep a hypothetical upside-down mail client from putting all of its control elements on the bottom of its interface?
First of all, i bet you that much more users click on a send button then press some arbitrary key combination.
Second i bet you that most people find the send button easier when it's somewhere they expect. Where the other buttons are.
Third, physical analog bla bla, really... Nobody thinks "hey i am writing an e-mail, that's just like real mail, EXCEPT i write on a keyboard, look on a screen and everything else i touch and see is not a physical letter or pen or paper at all!".
The real-world vs virtual-world comparison makes most sense for icons and such, in my oppinion. Not so much for workflows. You also don't ask people to walk to a virtual post box to send the letter. Or let them "stamp" it. Or as you said yourself, to sign it or to seal it.
Nothing keeps one from putting ALL controls to the bottom, a good interface may even accomplish that nicely. Except that it's only there to annoy people, restrain adoption and giving users a hard time figuring that out. You may be able to quickly learn that, i may be able to do that. My mother or grandmother? Not so much.
It'd be very interesting to see some A/B testing on this. Maybe i'm wrong, who knows.
It is weird to ask for the subject of an email before writing an email.
I'm sure I'm not the only person who has change (or left blank to begin with) the subject once I've written the email.
Also I've observed a lot of people who write the content first then fill out the top (To, CC, BCC) after. Often the content effects who should/can see the email.
The current UX is wrong given mis-sending, mis-addressing still occurs.
That's why i said A/B testing would be nice.
Because now i can tell you exactly the oposite of what you tell me.
I have 18000 mails in my work mail account (no spam amongst them, mostly "real" mail), 43000 emails in my gmail account (which is not even that old) and not a single mail with half-written content or whatever. This includes mails by extremely tech-unsavy people.
I also never did the mistake you mention myself, despite the UI so flawed.
And i've observed that most people start by adding the recipients first, then content, then subject and then maybe in the end they decide to add a CC.
So would a UI with To, then Content, then subject, then CC be better? Don't think so.
Also that interpretation of "the content effects who gets the mail" is REALLY flawed. It certainly effects if you add someone on CC, but not the person who you are talking to.
Atleast i know to whom i write a mail before i even open the mail editor. I also know to whom i want to write a letter before i write a letter. Maybe i am crazy or even psychic, knowing who i want to talk to beforehand :P
In the end i think your ideas try to solve a problem that does not really exist (not in my experience) or even if it exists that the disadvantage of confusing customers would outweight the minor percentage of people that would be helped by far.
I realise you've hit "someone is wrong on the internet" territory, and thus seem to be just ranting. But when you are telling me that peoples conceptual models of how to use email are flawed... you are losing credibility.
Computers should bend to people, not people to computers.
Quoting stats from your email accounts doesn't actually mean anything. You can't possibly make the claim you are making, only the sender knows if the email was 'finished' or not, not the receiver.
I didn't actually suggest any UI changes, only that existing UX (as in the experience) seems sub-optimal, because problems still occur.
Also, worst thing you actually can do is to put the save/send/ok button on the bottom when all other UI elements are on the top of the UI (which is usually the case in mail clients).