I live about 15 miles (less, as the crow flies) from our lake. Sunday, I was looking at the Windfinder forecast, and looking at tree movement out the window. I decided it would be what I call a "teaser" day, when there's enough of a puff to get across the lake, then you sit there and wait 20 minutes for a puff to get you maybe half-way back. I decided to have a slacker Sunday morning (at about the time I came to that decision, I also had a late Second Breakfast. It was more around the time for Elevensies, but apparently my Hobbit meal schedule is a bit off.) So, eventually I decided I needed a bike ride, and headed out for the 40 mile lake loop. About half-way through, I got a text from a fellow club member who lives farther than I do, asking if I was at the lake, and how was the wind? Heh, he got a video of racing in the distance, and my assessment "There has been a breeze, but not very consistent. I expect it would be sailable, but a bit of a teaser, too. Relaxing enough sailing."
Sooooo... short story long, there might be a market for such an app. The biggest issue is probably how to quantify conditions in a meaningful way, and how to build enough of a database or enough participants to get meaningful results. I believe there are plenty of friend finder or dating apps that show you where registered members are located with respect to your position. Probably not too hard to come up with something.