Well, java in debug mode can hot swap class methods, for what it worth. But the web is definitely the most used “GUI framework” ever, so there is no competitio

Well, java in debug mode can hot swap class methods, for what it worth. But the web is definitely the most used “GUI framework” ever, so there is no competition with that on tooling ground, even if there is nothing inherently that would block it, as a dom inspection is pretty easy to implement - just print out the tree of ui nodes.