Funny, I was just about to post a somewhat-related question to this board, and came across your post here (although it doesn’t quite address the question that I had, so I’ll still be posting that query, separately). 
I’ve been working on a blackletter font over the last couple years, based on an actual 17th century font, and I “made up” both Cyrillic and Greek/Coptic character sets for it because I basically discovered the same thing you did – after doing research on Cyrillic fonts from that period, they just looked SO different that I felt they’d be virtually unintelligible to modern audiences (and useless for modern uses). So I ended up just creating “modern” character sets for those essentially using bits and pieces from the Latin set.
I’ve posted my font (called “Wickednesse”) here…
…although after posting it (for the second time, just recently) I suddenly saw so many things wrong with it still, and have been working at fixing those things up. Oops! 
I think you may have seen my font? Your name looks familiar, I’m sure you’ve commented on a post of mine somewhere before, although I don’t see a post from you in this particular thread.
In any case, I’m thinking of just totally scrapping the Cyrillic, and Greek/Coptic, from my font because I just don’t know what the heck I’m doing with those, really – that was going to be my query (in another thread I was going to post), whether what I’ve done is “good enough” to keep them, or whether I should give them up. But in the meantime, I thought perhaps you might like a look at what I did, if for no other reason than for perhaps some ideas or something.
Good luck with your font, however it turns out!