There are a couple of parallel efforts ongoing. When I started this one:
my focus was on contacting devs and seeing what could be done. The main effort being to get them into chum as that became available. Those were not all harbour apps but some cross section.
In addition a growing number of things have been making their way to SailfishOS:Chum community · GitHub with @olf and @nephros also pushing in that direction. I haven’t done much (a couple of things, but should do more) and that has the advantage that resurrected apps would be under a larger umbrella org and hence more likely to find some level of support. So, where we can get to source, if the developer is not available, the strategy is to get the apps under the shared umbrella and at least make them available in chum. I’d go further and produce for harbour where possible.
There are currently 3 apps in my harbour queue that are blocked by existing old versions. Fahrplan SailDBmeter and Paint. All are available on chum and / or openrepos but for it would be nice to update the versions in harbour.
In the end, it’s mostly a communication issue. Someone has to contact, if possible, original devs and see if an app/maintenance of said can be handed over in coordination with Jolla.