The problem I have with that is it will drastically unbalance multi, mouse will end up with equal-to-best-turning, and best accuracy.
While technically speaking that was possible with the joystick, it took a hell of a lot of skill / microing to pull it off, and a lot of practise with max sense zero deadzone.
Freelanceresque (tachyon's alt mouse mode) shouldn't be allowed by default.
And if it's not implemented properly, it'll be worse than the current mouse model.
If you don't wanna use a joystick and don't like the fact that the mouses clear and significant advantage is it's accuracy then use the bleeding keyboard.
It's not hard.
Edit - to clarify, using the edited existing script that I think......Nuke? created, is fine, because that will set alarm bells off when used in multi.
Incorporating it into 'vanilla' shouldn't be in the remit of SCP, imnsho.
I may be overstepping here, but this feels the same as if I were asking there to be a keyboard equivalent of 'mouse smoothing' added to the game.
If there were I /probably/ wouldn't use it (because I'm so used to pro-actively counter-adjusting before my shot is lined up anyway and it would just put me off) but technically speaking it could make the keyboard insanely easy to use at a high level.
The three mediums for controls are all divided equally (well, mostly, joystick enjoys a mild advantage at the very pinnacle of skill from SW experience but it is very small and there isn't much you can do about it in terms of code either).