I don't find it that crazy, if properly compiled with web assembly. The thing is that Blender's UI is all synchronous python, so, yeah, that and the addons system would be to need rewritten. Python in the browser is a no-go performance-wise, of course.
> Python in the browser is a no-go performance-wise, of course.
"Running the Python interpreter inside a JavaScript virtual machine adds a performance penalty, but that penalty turns out to be surprisingly small — in our benchmarks, around 1x-12x slower than native on Firefox and 1x-16x slower on Chrome. Experience shows that this is very usable for interactive exploration."[1][2]
The main point though, is that running Python in the browser it's an unnecessary abstraction because you get a crappier version of something that runs pretty well natively. If you're starting from scratch, I think that the browser might be close to native performance in some tasks. Porting existing applications is a pain when you start looking into the details.
The problem is not so much the run-time performance of the code, it's the overhead of loading the Python run-time environment over the network the first time you open the page.
