Open question: How to deal with buffers that need lots of reads/writes

There are a few cases where we'll have buffers that need to take lots of reads/writes, and are not in linear memory.
Examples include gpu-buffer when mapped to CPU, and frame-buffers.
How should we go about those?
Here are some options I've thought of, none of them seem particularly good to me:

• Just copy everything over as list<u8>. Obviously slow.
• Have an external resource, with .get()/.set() methods. Prob slow since every .get()/.set() will have to cross the wasm boundary, but might still be best option with current capabilities.
• Find some magic way to map it to linear memory. Don't think this is actually possible.

Thoughts anyone?