Create a UI design toolkit that allows you to draw a user interface with divs that can have background-images that are bitmaps; and that's already a feature of HTML.
Create an object class accessible through scripts that mirrors the object structure of HyperCard. You just have to get out the manual and clone what they had.
I'm not in any way a good person to lead this, btw. I didn't spend much time with HyperCard, I was a C programmer at the time, and working directly with the Macintosh operating system, without an intermediate layer. I created a different environment, Frontier, that never got a graphic design tool (we tried) so when the web came along it was a perfect fit for us. In other words, I went in a slightly different direction in the early 90s.
I think my friend Ted Howard tried to do this a while back??