For anyone considering building a business as an integration provider on top of Embed.ly (the only way to get embedded on Medium), you may want to follow the advice from the founder, Sean Creeley, who just sent me this:
"If your whole business relies on us, you might want to pick a different one.".
TIMELINE:
1) I ask Embed.ly if the novelty factor (existing competitor) would be an issue before building an integration for them
2) They say it'd be ok, as long as the other guidelines are met
3) I spend a month building the initial MVP and send it for approval
4) The founder replies and instead of providing guidance on what should I change to get approved, accuses me of "copying someone else's work" and that "We aren't going to argue with you on this".
Screenshots of all conversions (newest at the top):
http://imgur.com/a/7nfPC
Make your own judgment.
At the moment, you're claiming that 'novelty' is the choice of consumers to choose a different product. That's not novelty, that's competition.
Their comments are entirely reasonable - submit it when it has something new to offer. You say that you have these ideas - and if you truly believed in what you were doing, then you would put this time in upfront on the product on the speculation that it would be so good, they could not turn you down.