On a gaming site that caters to your genre, probably.

I was thinking specifically on GDnet. We have an announcements forum, but that's mostly for final releases. There's the Indie Projects forum, but it also seems to be final releases.

if you want feedback from gd.net then your best bet is developer journals tbh. but to be blunt, gd.net has never truely been about giving feedback on projects(YA subforum is generally the same person posting in the thread about their own games, and every now and then another person will chime in). i've had success on chat, but i also spend alot of time in chat, and know alot of the folks, so when i ask for help, they are willing to lend a hand(or i don't feel bad about bugging some of them), and i've seen others get feedback there. however if someone isn't a regular it's really a crap shoot if you'll get people to be interested enough(and trust you to dl an exe) to give you feedback.

Overall i have to agree with Graelig, GD.net is just not a great place for asking to get feedback on demo stuff(but maybe you can try design/idea subforum, and ask a mod not to kick it to YA) if your looking for valuable feedback, i'd look for forums that have a more dedicated gaming community, of course if your not apart of those forums, just popping in and asking is not really going to get you anywhere(unless your demo is super amazing). Good luck with finding help though.

Steam Early Access

Best bet is probably the Developer Journals or Game Design, although in Game Design it'll need to be worded so as not to look like a stealth announcement and get moved.

Could we setup an "Ongoing Demos" page like we do the "Image of the Day"?