I'm very curious about this tsumobi thing, as it's basically exactly what Hecl is ( http://www.hecl.org ). I'd sort of abbandoned it as an idea for making any money with directly, though, figuring the advantage was just to be able to develop applications a lot faster. I was able to prototype ShopList ( http://shoplist.dedasys.com ) in a few minutes with it, for example.

Edit: BTW, I'd certainly be interested in chatting with the Tsumobi folks. It's a good idea - perhaps there are elements in common that can be reused from/added to Hecl, which is open source under a very liberal license, meaning you can take it and include it even in 'commercial' apps.

I really think that the 'common' bits in a space like that have to be either free or open source (think about browsers, html, javascript, java applets, etc...), and that that's not where the money is.