I think the only thing I genuinely miss from Misskey, which I wish was just like a "standard feature" of all Fediverse software, is Misskey's user drive feature which lets one directly manage one's uploaded content, treat it like a form of cloud storage, and select previously-uploaded files for appending to new posts thereby solving file duplication. I know that Mitra ostensibly has a sort of file hash that should prevent file duplication of exact file copies from being stored, but it is a bit different. Misskey is a bit "overkill" for a small instance like mine, and Mitra fits perfectly. However, that's about all I really miss from Misskey. Not to say that Misskey isn't phenomenal software itself---it would be my first choice if I planned to host a larger community. Mitra is perfect and ideal for smaller communities. Different tools for different applications, I guess.