HTML5 needs... gaming, game-pad support ( I have already seen this, but this just started ), much better full screen ( also know this is being worked on )
it sounds like most of the problems you have are indeed being worked on, and this is just what you've heard of. you're not the only one who thinks the platform is incomplete. html5 isn't even done yet. I would say everything's moving amazingly quickly, as everything always does in the computer world. I mean, I didn't even hear about webgl until fairly recently, and now it's already supported on the chrome beta for android. adobe abandoned flash because of html5 and js(there are flash games on steam). There are plenty of big players who are looking to make it faster, better, etc.
as far as very old machines? even construct classic requires dx9, and though there were a few people complaining about that, almost anyone can run a construct classic game. the best supporters of older machines in the industry as far as AAA titles go I'd say would be valve. and you'll notice some of their newer games, like portal 2 and left for dead 2(which was released a little over 2 years ago) don't run on older machines, at least not at any playable framerate. valve is known for their games having reasonable system requirements.
ow long does this seem it's going to take?
I don't think any of us know, probably a little while. my own personal pessimistic prediction is that within two years, some combination of these web technologies will be comparable to flash speeds, but I think 1 year is closer to the mark. also, I can't speak for scirra, but I'd think within 5 years, work on the next exporter would be begun, or the edk, or the web platform will be approaching the needed maturity. if you need exe's support now, honestly, use construct classic. It's got your working audio, game pad support, full screen, exe, etc. especially if you're planning to develop a game so quickly that you're concerned about waiting a year. it's already been stated that native exporters and/or the edk are in the cards. C2, js, and html5 are being worked on hard by people that are probably much more diligent than ourselves. it's not going to arrive faster by being upset it's not here yet. Honestly, cc is probably your best bet, or if you want to sacrifice alot of ease of use for more crossplatform compatibility, Unity is your best bet.