The Champions League has been many things in its existence. It started in 1955 as the European Champion Clubs' Cup, a simple tournament to determine the "best" team in Europe, and was comprised of 16 teams, each of which, as the name suggests, was the champion of its domestic league in the prior season. The tournament was a straight knockout, and over the years it was expanded from 16 teams to 32, but otherwise didn't change much until 1991, when it was rebranded as the Champions League.
The tournament continued on in its original format until the 1992/93 season, when it was constricted to 24 teams but expanded to include a group stage prior to the knockout rounds; this proved so popular that UEFA added a second group stage that ran from the 1999-2000 season, which also saw the Champions League re-expand to 32 teams, until the 2002-03 season, when everyone realized two group stages was one too many. The competition dropped that second group phase and has held firm to the one group stage, 32 participant format ever since.
But now, there are Rumblings. Rumblings of change to the format that would come into effect in 2018/19, to be precise. This is the high level summary:
And the Guardian has more details. Basically, what is being proposed is a smaller group stage with more games - half the teams (16), more than twice the games per team (14). The net effect of this would, of course, be to isolate the Champions League further away from the pesky little Malmos and Apoels and Bate Borisovs of the world, who had the temerity to try and crack the Top Club Club and siphon away some of that sweet, sweet Champions League money from the jaws of Barcelona, Real, and the other traditional powers of Europe.
There would also be some other structural changes, including additional knockout rounds prior to the group stage, which would see the top teams unable to play each other until that renovated group stage. This, of course, would also weed out a lot of the lesser lights and further preserve the Champions League as effectively a closed league, and as perhaps a first step towards establishing an actual closed league.
These changes are still three years away, so there's nothing set in stone yet, but it does seem like the deck is being stacked against what in NCAA terms we'd call the "mid-major" teams yet again.