[eckzow]

In re your first bullet: If such things are important to you, it looks like you can produce fixed size packets through a variety of methods. In particular, they support overlength encodings.

[bkirwi]

True; but it's hard to support a fixed-length encoding when a message can contain nested collections of arbitrary length.

[drosenborg]

The just released Blink Native binary format might be an alternative if you want a fixed-length encoding: http://blog.blinkprotocol.org/2013/01/blink-native-format-re...