It is never a good idea to assume that a can opener[1] will always be available. While your decoder - an extra tool - may be available in "many" cases, there will always be a sizable minority of cases where it isn't. As the performance benefits of fixed-width fields are orthogonal to the fields being ASCII-vs-binary.

> SCTP / "transport-layer protocol"

So we move yet another step down the path of obsoleting TCP port numbers by adding another layer of indirection[2]. Re-implementing ports by tunneling everything over HTTP{,2} was a bad idea when it started over a decade ago, and it's still the wrong way to solve the problem.

[1] http://en.wikipedia.org/wiki/Assume_a_can_opener

[2] See RFC 1925, Section 2, rule 11a. ( https://tools.ietf.org/html/rfc1925 )