In Software Sources, currently you can add / edit / delete PPA's. Mint Team made it trivial to add PPA's and even fix some of PPA issues.
Am thinking if it is possible Mint team (along with community support)to maintain a list of popular PPA's and search for the applications /software.
It may seem to be a Herculean task to track the changes in PPA's and check if they're active or not but with strong support from Community and with a rating system and user feedback for PPA's, this can be built as a repository over a period of time.