[Updated: I see that lat/long entry already exists in iFly. See bottom.]
If iFly wants to implement a feature to accommodate this request, I don't see any downside. But as it goes to priorities, frankly, I've never had a need for what Larry is asking for.
Back in the old days (before Internet), I used to pull out AAA road maps and match them up to a Sectional to find an airport to fly into. Or I would call my destination and ask the locals if there were any GA airports nearby. (If you want to attend one of the Golf Tours in Tucson, the locals will tell you to fly into Marana. (Not Tucson Int'l.)) A phone call is how we found that we wanted to fly into Sugar Land, TX on business in Houston.
But I took his three locations challenges, to try to see where he's coming from. I still don't see it.
Now that we have the 'net, I was able to find solutions in about a minute each using AirNav or Google Maps. (I don't understand the need to get an answer "quick." It's not like an in-flight Emergency.) I'll run thru my solutions in a moment.
But first, even if iFly had the ability to find the nearest airport to a street address, the nearest airport isn't always the one I want to fly to. Runway might not be adequate. No fuel? No restaurant or rental/crew car? If its' private, the odds are that I don't have permission to land there. That is, I don't always fly to the airport nearest my destination.
As an extreme example, we had business in DC once. Having flown into BWI a few times before, and not liking the prison atmosphere of the airport, we opted instead to fly to an nice relaxed friendly GA airport 30 miles away.
Okay, so for his challenge.
Taking the last first, I typed "Blue Ridge, GA" into AirNav and found 57GA. It's private, so might not be an option. No fuel either. But AirNav shows METARS for other close by airports. I would probably land at Gilmer. The Interstate takes you right to Blue Ridge in 20 minutes.
I've never heard of the Lawrence Welk Resort. So I did a web search. When I saw it was in Escondido (CA) I knew, from having been there before, that Carlsbad Palomar would be my choice. Google maps would have told me the same thing.
The hardest was Carmel, IN. AirNav doesn't give a result for that. I searched the web for Prairie View CC, to find the county it was in. Still no joy in AirNav. So I had to type "Prairie View Country Club" in google maps. Once I saw that it was NE of Indianapolis, then it appeared that Noblesville was a candidate. Now that I've gone thru the exercise, I would probably just go to google maps first for the info.
So for me, this was kind of a fun puzzle to solve.
Having said that, as has already been suggested, it seems like the easiest solution would be to the have the ability to paste lat/longs into the Search box in the iFly apps. (Or perhaps in addition to a "text search," a "lat/long search"? Although what format?) That way, a user could copy a lat/long from google maps on their tablet (won't help the dedicated box users), paste it into the search box and, just like tapping the waypoint Instrument when there's a lat/long in it, iFly would move the map to there so the user can see visually what airports are near by. [Per my update: most of this is already done in iFly.]