The whole idea of Area 51 and giving chance to people to propose their SE is truly amazing and probably the feature of SE I can give most praise to ( otherwise most praise goes to ever hardworking moderators ).
It is only natural that Area 51 ideas that don't receive enough attention and activity are deemed "not the right stuff" for the SE network. However, some ideas that truly are great don't shine because of the inactivity during the testing phases - but doesn't mean the opposite can't happen in some years hence.
We all know about certain topics and areas that strike the world and gain instant popularity and recognition. But there are also topics and areas that do it by a steeper path, for which it takes a longer time to achieve (near?) equal popularity.
Therefore my question is : Can some 'failed' Area 51 proposals get another chance after some time ?