The new architectures include more and more data exchange among databases. Now when you deal with bigger data sizes that go from millions to billions, this fixed size vs of text - undefined size becomes very relevant.
Can you demonstrate, with actual numbers, using today's implementation, a situation where defining a column as char(3) or varchar(3) instead of text has a significant performance improvement? Without a concrete example to examine I'm unable to be convinced to move away from the status quo.
You also need to convince me as to why constraints are an insufficient feature. i.e., why is char(3) better than (check length(val) = 3)?
Even with all that I'd probably still not do anything beyond reviewing a proposed patch (i.e, I wouldn't try to write one myself from scratch...I don't have authority to commit regardless).