Hacker news for problems would be great then.
Of the two, the latter is probably the better option. Perhaps I list a pain point along with the amount I'd be willing to pay to have that problem solved. Others do the same. There's no tipping point because it's unlikely that by simply having a problem I'd also know how much it would cost to solve the problem.
At any point, users/companies with the skills to solve the problem can propose solutions along with their minimum funding requirements and relevant credentials. I can select more than 1 solution and whichever solution reaches their minimum funding requirements first gets my pledge.
Or instead of trying to compete with kickstarter, this could simply be a step that happens before campaigns are launched on KS. People list their pain points and the amount they'd be willing to pay to have them solved and then you charge companies to add their solution/link to their KS campaign.
Good idea to see it as an addendum to an existing service rather than a service in its own right. Or an amalgam might work, whereby the "kickstarter for problems" is a separate service, but on reaching the tipping point the project morphs into a regular kickstarter project, that has already reach its tipping point. This would require each backer to also have a kickstarter account (if not the kickstarter project would come up below its tipping point), but it would save a minimum viable product from the complexities of having to handle money.