I have a few thoughts to throw into the discussion.
First, I believe that with today's taper lapped barrels it is often mentioned that it takes about 1000 rounds to "break in". I think if any change occurs, its in the chamber leade area and not the balance of the barrel itself.
I have had polar opposite results with the "break in" on new barrels. The first new barrel was installed on by Karl Kenyon and it shot incredible right out of the gate with no change over it's competitive lifespan. Another subsequent barrel that performed just as well (installed by another 'smith) did take several bricks of ammo to reach the peak of it's performance. With that said, the "change" was very slight.
Second, as for "seeing" a change after 2500 rounds, I would have to ask this level of "change" and if this is not just a case of measurement error or are the results in the area of white noise of lot shot to shot variation. The test set up to see such a change would definitely have to effectively exclude human and environmental factors and the measurement techniques would also come into play.
Finally, I had a discussion with one of our Olympic champions several years ago about the barrels she was using. She was using an Anschutz 20xx series action and had a collection of barrels from Lilja that she rotated for training, matches and international level matches. She noted that the accuracy of the barrels had changed over several sets and that the last few were degrading notably after 17-20k rounds. Apparently, she was told that a softer steel was being used and that was causing the faster degradation. I can only present what I was directly told, however very soft stainless would machine easily but also wear faster.
I would certainly be interested in the topic of barrel wear. With that said, the variables, test methods and measurement techniques may result in a daunting task.