> text display, scripting, styling
The only thing that really matters is scripting. Every serious editor has solved displaying text and styling since ages and those two points aren't even that important in programming languages. All you want is a syntax aware highlighting. Maybe underlines and a little bold here and there.
Scripting is the really hard part. There are many flavors, languages, APIs to chose from. Just because you now can script things in <hip-language-of-the-day>, the problem isn't solved. My editor uses a lisp dialect and I'm perfectly happy with it, not because of the language choice but the APIs and amount of integration.
One thing that is incredibly important for text editors is speed: something web engines are notoriously bad at.