This already exists.
https://www.uspto.gov/patents/initiatives/third-party-preiss...
Note that I'm not aware of any way to challenge an application on non-prior-art grounds like 101, 112, etc. But I imagine emailing the examiner assigned to the application would work. Unfortunately examiners aren't assigned until a few weeks to a few months before examination, so a challenger will need to periodically check the status of the application before contacting the examiner.
You can look up the examiner's phone number here: https://portal.uspto.gov/EmployeeSearch/
Email addresses are typically firstname.lastname@uspto.gov.
What I propose is that anyone can submit solutions to the original problem stated in the patent, without yet knowing the solution proposed in the patent. This allows us to demonstrate that the solution is trivial to those who are skilled in the art.
In practice, almost no third parties submit prior art, which is a lot simpler than submitting solutions. So I doubt people will submit any significant amount of solutions.
With massive amounts of money, since the PTO has made it impossible for the system to actually be fair.