There's a little bit of contradiction in your desires: you say you want to keep "exactly the same theme and plug-in structure" but you also want to limit backwa

There's a little bit of contradiction in your desires: you say you want to keep "exactly the same theme and plug-in structure" but you also want to limit backwards compatibility. You also say you want to remove bloat and non-core features yet you want to bundle a load of questionable plug-ins. The nicer interface and UI would be welcomed, but I think if you start going too far you'll detract away from Wordpress's core appeal. Don't forget there are many alternatives to Wordpress that have more features built-in, but Wordpress has succeeded because it's simple, flexible and easy.