I don't buy it that you tried everything open source had to offer but I do agree that kdenlive is pretty... eh... never used it but the little I saw from it didn't make me feel they're about to change the world of editing.

Even though it's not Open Source, davinci resolve has been pretty good to me, even the free version, it's sick bro you should try it out! Even if you do feel like you'd rather make your own software suite, you should at the very try to take a few notes from davinci Fusion, your users will be thankful:

- having a node representation for compositions has some drawbacks but massive advantages when it comes to visualizing and organizing scenes - copying nodes/layers/effects and getting plaintext in your clipboard is EXTREMELY powerful and underused, it basically means that any text manipulation becomes potential automation. This is a super cool feature and even though I will not use your software, I think you should look into it!