I have noticed, there are a few dead beta sites that I thought were really good ideas, but just didn't have enough of a community to support them.
The problem with dead beta sites though, is that it stops those sites from ever being created again in the future. If one were to create the proposal again, it will usually be marked as duplicate, and closed.
What I propose, is to have something on the proposal, to allow for users to vote to re-open it. If a certain number of users vote to re-open it (I think it should be about 1.5x the amount of people needed to commit to a normal site for it to go into beta), then the site would be (completely) re-opened again.
I do not believe this is a duplicate of this, because that is asking if it is ok to create a new proposal to see if other people want to re-open the site. This post is a feature request asking to allow users to vote to re-open an existed dead beta proposal.