As a developer, I can only give my insight in to the process. My considerations would be:
Will adjusting the app break other functionality?
What are my current deadlines?
Is the App making me enough money to justify the coding and testing time to update the app?
If I answered; No, none critical, yes then I could see the app being updated in the next 1 to 90 days. But if any of those were opposite, then the odds of updating are very slim to probably none.
Remember, not every app updated to Retina display quality and that has been out for years now. So don't expect every app to adjust for a third resolution.