Cool stuff, I've considered building something similar for my own needs. For me, I would never invest the time to learn and integrate something like this into my business processes if its not open source. But there is a large market of folks who don't care about that (obviously, as Salesforce isn't open source and does well enough), so you have a lot of potential.

I played with the demo for a couple of minutes- one thing I noticed was that to add a field, you have to go up to the drop down menu in the top right and select add field- I would expect to see an "add field" button below the (initially empty) list of fields on an object. Hotkeys would also be really nice at some point as you develop the app. Probably just really early in your development to refine these things.

You mention your path to success being a "modern UX" and I think that is great, if by "modern UX" you mean (at least in part- a major part) "much faster and more responsive than Salesforce". Maintaining the flexibility while also keeping it easy to use and fast is a triple combination of power.