The first three all have the same story though, where Oracle acquired the project, forced changes that drove the original authors out, who then forked the project and resumed development there. So Hudson/OpenOfice/MySQL essentially lost the key developers that had all the institutional knowledge, killing them.

I do think there would be a lot to gain to merge vim/neovim, but they're in a very different position. I don't know enough about the other two forks to draw parallels to them.