You just described "a couple decent developers + ruby on rails + custom development".
The interesting bit is trying to create the next Excel or Access. The most recent (aborted) attempt was DabbleDB (http://en.wikipedia.org/wiki/Dabble_DB).
Well, no, rewriting from scratch in Ruby is not, in any way, equivalent. If you're going to rewrite from scratch, by all means, Ruby seems to be the way to go. But that's way too expensive and risky. What people want is to take their current app and make it happen.
DabbleDB failed because it was trying to completely replicate Access, without being compatible with Access. And no, uploading your data is just not good enough. Access is not a crappy mysql; it's an IDE with a GUI editor and a programming language and a crappy mysql. DabbleDB was just a crappy mysql.
The huge business opportunity here is not to compete with Access. It's to let people leverage their existing huge - monstrously huge, seriously - investments in Access databases, adding just enough functionality to keep it alive.
Once you have the cash cow taken care of, then sure, see if you can add some features and replace Access entirely. But then Microsoft will probably not like you as much.
The interesting bit is trying to create the next Excel or Access. The most recent (aborted) attempt was DabbleDB (http://en.wikipedia.org/wiki/Dabble_DB).