The problem they are trying to solve is that the programmer could forget to wrap an object creation with try. But their solution is just kicking the can down the road, because now the programmer could forget to write "using"!
I was thinking that a much better solution would be to simply add a no-op default implementation of dispose(), and call it whenever any object hits end-of-scope with refcount=1, and drop the "using" keyword entirely, since that way programmers couldn't forget to write "using". But then I remembered that JavaScript doesn't have refcounts, and we can't assume that function calls to which the object has been passed have not kept references to it, expecting it to still exist in its undisposed state later.
OTOH, if there really is no "nice" solution to detecting this kind of "escape", it means that, under the new system, writing "using" must be dangerous -- it can lead to dispose() being called when some function call stored a reference to the object somewhere, expecting it to still exist in its undisposed state later.