I'm sorry if I implied that curl/wget handle this already. However, they could handle this with a very small wrapper script, maybe 3 lines of code, or a very short patch if the convention becomes a standard. That's not nothing, but it's maybe 7 orders of magnitude lighter than a full JS engine, and it's small anyway compared to the number of cases that a reasonable crawler needs to handle.

Also, with that wrapper or patch, curl & wget will still not be remotely HTML5 ready, which I hope demonstrates that HTML5 is not a requirement in any way. A single HTML5-non-ready browser that can't handle this doesn't mean therefore that HTML5 is a requirement.

They aren't? You're only supposed to use them if you follow Google's convention, in which case they should be reliably replaced with a normal URL sans the hash. Of courses your scraper must be aware of this, but it should be a somewhat reliable pseudo-standard (and it is just a stopgap after all).