For tomorrow's mid-week PHL-PRG flight, I see the following open seats on AA.com:

2 out of 20 are open in J
10 out of 21 are open W
35 out of 206 are open in Y

In short, the flight is 81% full with a very solid occupancy in J. This is a mid-week flight before holidays start in the Czech Republic, making me think the route is starting to do very well. Also, fares are rather high compared to other EU connections to North America.

One day later, there are only 3 business class seats available, 15 premium economy seats available (might this cabin need better marketing/prices?), and 30 seats available in economy. On Friday, June 28, business is fully booked, with 1 seat available in W and 26 seats available in Y (89% full).

It seems to me that while there is certainly potential to grow, the route is doing very well. I would personally be thrilled if AA considered an extension of its service to PRG throughout the year, potentially on the 788 during the off-season when they get additional deliveries. Together, with Qatar and British Airways, oneworld can provide the much needed long-haul feeder flights to/from PRG to the rest of the world.