If the iPhone 6 brings out another screen resolution (as much of the current speculation thinks it will) that may further highlight just how many Apps have been abandoned.
For my company, there will be a select couple of apps that we would update for release--or try to get updated in time for release as long as it can fit with our other work schedules because none of us are full-time anymore.
Certainly FTP on the Go (Standard, Pro, Pro-Upgrade) would get updated quickly. But that is not a graphics based app. It's all windows and pages that will resize automatically. It will probably just need the new icons for the app and toolbars. Easy.
ContactClean (Free and Pro) will get an update, but these are also not graphic-based, so would be quick and easy to do. These also typically get a sales boost when new phones are released.
The games are not so easy and will get through eventually. At least the ones that sell reasonably well.
World1-1 will just scale-up since it's 8-bit pixel art to begin with. That's helpful.
Poker Apps (Holdem, Holdem-Free, Omaha, All-In) would probably get done next, but would mean exporting a lot of card and chip graphics for all the new sizes, which is time consuming and boring but not very hard. The source graphics are all either vector or plenty big thanks to retina iPad so there won't be problems with the sources not living up to the challenge. The exception would be some of the card protectors, which may just have to scale up and people live with it.
Not sure what gets done after that, if anything. Pawn'd? Bloc'd & Bloc3d? Knife Dancing?
Any game that uses non-vector stock art may take longer if it gets done at all since those can be harder to scale-up depending on the source.
If I had to guess: if only the top 1000-2000 apps overall (0.05% - 0.15%) got the update to fully support the new resolution then most people wouldn't notice or care that the rest haven't as long as they scale up and don't look to pixelated.
And Apple better make things work pretty good in the new resolution because there are going to be a lot of apps that will not get updated.
Apple's press will talk about the mad-dash to update apps just like ios7. And how many thousand get there before release day. They won't mention the million+ apps that won't get there by release day and probably won't get there ever.
Finally, as I said when retina first started going into devices, if we have to include different graphics sets for @1x, @2x, @3x(?), HD, HD@2x, and HD@3x(?) then that's a lot of excess baggage since any one device will only use a single graphic set.