[sciurius]

As embedded directives are not (and have never been) part of ChordPro, I assume that the text will come out ‘as is’, so

Code:

And [C]then we {loud all sing} [F]hello

will come out as

Code:

    C                       F
And then we {loud all sing} hello

As for {loud}...{/loud}: I'm afraid this will soon become too cumbersome. After all, we're musicians, not HTML writers.