One obstacle to replacing proprietary peer-reviewed journals with open alternatives is the difficulty of getting good peer review.
The approach of having authors pay publishers to arrange the peer review will probably have some success, but appears to be a recipe for much slower than optimal migration to open publishing due to the incentives it provides for authors to stick with proprietary journals.
More radical alternatives usually raise doubts about whether their quality will rival traditional peer review, due to lack of incentives for someone to ensure that the peer review is done by disinterested peers.
My idea is to have a system where anyone can review papers that have been registered within the system. The reviews would be made public, without identifying the reviewer.
The system would reward reviewers with a reputation. Reviewers would have their reputation score increased if a paper they positively review is widely cited, or a paper they negatively review is retracted (by a larger amount, to offset the lower frequency of this result).
It ought to be possible to convince universities to give this score some weight in tenure decisions, and if so that would ensure an abundant supply of reviewers who are at least as objective as under the current system.
The simplest implementation of this would impair the anonymity of reviewers by enabling people to connect changes in scores with the timing of citations and retractions. That could probably be dealt with by adding a random delay before a score is recalculated.