I think they probably can. It's just that we've been convinced they can't by people like Adam Back who have a kind of religious belief that bitcoin was a "one-off event'.

I think you'd find that if technologists really wanted to create a unified, scaleable, instant monetary medium based around a single blockchain then they probably could if they weren't all ego maniacs that thought they were saving the world from financial oblivion rather than just solving another day to day technical problem.

The difference between holding something in your hand and holding a promissory note that says you have it "in your hand" is something that the general public understands very well and if that is the basis for bitcoin's so called "scaleability" then it will only open up markets for electronic assets for which it isn't. Thats all I'm saying.