Here's another idea for
@FiiO or any other manufacturer lurking in this thread (if you like it I want a cut of the sales
)
How about implementing ANC in a DAP? Just like on ANC headphones, the DAP would just need a couple of external microphones built in, and if turned on, would work just like any headphone ANC mechanism. Yes, it would have some obvious limitations (might not work well if inside a pocket for example) but otherwise it can be a great, unique feature that can turn any headphone to ANC. Would be perfect for use in flights or public transport for example.
Can be a nice distinct feature if any manufacturer picks this up!