This would allow for efficient allocations in plugins, such that they can do an in-place new() on a chunk of memory (iobuffer).
The API / features should make it easy and possible to asks for an iobuffer of at least size <x>. It can return a bigger one, at which point, you'd waste some. But this allows us to reuse / repurpose the existing iobuffer allocation.
Phil points out that there are existing iobuffer allocation APIs, so maybe something in conjunction with that is appropriate. I would like for this to be easy on the plugin user though, such that it's as simple as "malloc/free" chains.