[c3RlcGhlbnI_]

How much of the power of sed does it bring?

I feel like other sed expressions might be even more useful in this format. For example:

    200i #TODO optimize this

will insert a comment before line 200 and:

    s/.*goto.*/cowsay \0/e
    T
    s%^%//%
    s%\n%\0//%g

will take every line that contains a goto and replace it with a commented out cowsay version of itself.