@renchap Quote can be represented as Object Link with relation type https://misskey-hub.net/ns#_misskey_quote, this is what Threads and some other projects started using. But yes, this part has not been specified yet.
What issues do you foresee?
I'm adding rel="https://misskey-hub.net/ns#_misskey_quote"
AFAIK Streams and Pleroma doesn't add rel at all, so Mitra would accept any FEP-e232 Link regardless of rel value (as long as it points to something that looks like "post")
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