Origins should be restricted to eight bytes

[olorin]

• Variable-length fields cause all sorts of problems in practice (most immediately, I can't implement fixed-width telemetry messages).
• This doesn't limit practical applications; if you need more than 2**64 data origins in the next hundred years you're doing something very wrong.
• Six bytes is the convention, but there's no point wasting the last two bytes of the word.

This is a breaking change, so I suggest it be slipped into v3. For now, I propose a documentation change indicating a limit-by-convention, and that origins in telemetry messages be truncated to eight bytes.

[istathar]

+1