Disclaimer: This is not really an answer, but a bit long for a comment.
What would worry me about using unicode characters directly is that the command might expand to more than just the character. This is particularly the case in maths mode. As an example, ∘ is, as a unicode character, simply a letter. However, mathematically it's an operator. Is the unicode support smart enough to know that in maths mode, f∘g should have a little extra space in it?
(I want to add that I don't think that it should be that smart. For the same reason that we have
<, then ∘ should be simply the character with the default spacing and
\circ should be the operator. Borrowing from MathML, ∘ should expand to
<mo>∘<mo>. So the behaviour that I would like is that é can be used for
\'e if they are syntactically the same.)