If you could get out the key blanks for 30-50 dollars with customization options like your keychains I think they would be a big hit. I hope you can bring something to the table because I've been searching for an NB key that is not ugly for quite some time.
Hell even if you just did something like this I would be ecstatic. Hopefully you will consider some option!
oh and one last thing...are you thinking about designing something for the nb/nc owners thats not as retro looking? If not I'd still buy a key with maybe the blue mazda logo but you haven't made too much that screams perfect for a non NA miata to me. maybe something featuring the newer M logo?