Such an initiative really doesn't require an independant website. We could just simply leverage the existing facilities to setup our own "workshops and symposiums". Experience suggests the least you rely on them the more successful, and more rapidly approriated solutions occur. Quite a lot would fit in the existing forum structure. Might be "better" if get some mod/admin to open up a specific subsection for somewhere. Possibly MoS » Technology would be deemed suitable. Or maybe in MoYaE » Education. This ideally wants doing for a wider range of topics than "programming" - although this one will enable us to build for everything else.
I've heard rumours we're supposed to be getting "collaborational tools" which would be massively beneficial to such an initative - I also put in a feature request for a wiki, not overly sure how eager that is to be adopted but it'd also serve well this purpose. I'd also suggested a sensible comms protocol be deloyed - like XMPP - which should provide for everything else absent to make what you'd suggested realistically achievable. Even more so if these services was to be tightly integrated. I can't recall if I'd specifically requested git, I'm sure I should of, but that'd be handy too.
Until the existence of such however I would suggest opening a post in the feedback section specifically requesting somewhere to place this - as previously suggested, this could tidily nest in an existing subsection - it might be beneficial to include a loose structure you'd expect to see inside the subsection. I'd personally envision this at least subsectioned further by language.
As to a bit like linkedin - sort of, but less invasive. Less easy to be utilised to bolster OSint and definitely not associated with any of the data collection/utilisation practices engaged in by microsoft as they desperately claw at more personal data in an effort to gain ground on companies like google and facebook.