Current design is reasonably simple and compact, but we have two major issues:

1. Alignment is fixed at double-usize (8 bytes). It'd be nice if we can at least align to 16 bytes, and this might give us up to 32KB alignment for "free".
2. Payload size of 2^n - 8 is super clunky. A lot of my personal usecases require 2^n exactly, and having this limitation requires an extra half page to a page.