Overhead would be in:
1) Teaching ALL participants about job to fill.
2) Dealing with job seeker's frustration when he would need to answer the same questions to different people in the process.
3) Restricting access to potentially sensitive personal information.
As the tasks get completed the next step happens, and the site manages the whole process.
The job seeker would not have to answer questions at each step of the way. The information would be saved in the system so that each person managing the step (whether internal or outsourced) can see the output from the previous step.
The steps are something like : write ad, sort responses, initial screening, organise interviews, interview, negotiate offers. The company would choose which of these they want to handle in-house, and which they want to outsource. You could come up with a few templates to cover a large proportion of hiring in industries.
Restricting access is just done with the same types of legal terms that existing recruitment agents use. The site would include a reputational factor, the same as any other online marketplace. So someone who wants to have a at-home job sorting through CVs isn't going to start leaking the information if they want to get more work from a client.
Ideally the jobs would be listed on the site itself, but there's no reason it can't be used to manage jobs that are listed on existing (and popular) sites. The idea would be to leverage the network effect of other sites while building a base of clients for the site itself. So initially listings would be on the site as well as other popular sites. Over time, a strategy would be devised to drive the popularity of the site itself as a place for jobseekers to find work.
If so many users access your information - how do you know who leaked your sensitive data?
Outsourcing such small pieces could make sense only to the web site itself (which is fast, cheap, secure and reliable) - not to external human players.
Traditionally humans tend to manage computers, not the other way around.
5) Outsourcing the DNA of the company to the lowest bidder.
If your idea or your management team suck a recruiter can only do so much. Once you are worth your salt you can hire one full time recruiter and be done with it.
Recruiting is more important, not less important. Commoditizing it means you don't know how to build a company.
On (4) this is a fatal flaw unless the market can provide enough liquidity that there is fast turnaround on bids. Overall I think it is a killer of the idea.
On your (5) I would say that many organisations have no DNA worth speaking of. This is the market I would be speaking to.
I have done contracting work for many different companies over my years. Rightly or wrongly, it's seen as a cost centre rather than a strategic issue in many cases (despite the rhetoric, of course).
What you get then is a bunch of randomly selected people (essentially). They really could be random given the fact you could have many different "recruiters", without any true consistency on how they were chosen outside of process.
A hiring manager could use this service for a handful of hires. Individually all the employees look great on paper. But something weird will happen when you put them all on the same project, and you are going to wonder where you went wrong.
Personally, I wouldn't see a web application commoditizing the hiring process as disruptive (in any good sense, anyway). LinkedIn was already disruptive because it changed the recruiting industry and well-qualified highly-skilled people don't stay unemployed long because of it.
Recruiters jumped on LinkedIn because it was built correctly and it made their job easier. Trying to commoditize the process further is going to be difficult because any recruiter worth their salt isn't going to take a pay cut and fight for bids. Most recruiters I've worked with take a commission on the hiring salary anyway.
I understand that the concept is disruptive from a hiring managers point of view ("Great, I don't have to hire HR, recruiters, or pay out the ass!"), but my guess is its going to be difficult for them to take the jump into an untested service to literally have anonymous bidders ala ebay doing their hiring.
As a manager myself I wouldn't use such a service.
