Big McLargehuge
Fragile Traveler
I think that day is coming. With construction costs the way they are, and with political climate leaning against public funds for arenas, you'll see smaller arenas pop up within the next couple of decades once the current arenas start to reach the end of their useful lives, since ~19,000-seat arenas, at the current cost of construction, are too expensive for a lot of private investors.
We saw this with baseball stadiums. In the 60s and 70s the old stadiums were deemed too small, with their capacities hovering around 30,000 on average, and they were replaced with stadiums that were 50,000+. Those stadiums aged horribly and were replaced in the 90s and 00s with, generally, much smaller nouveau retro designs.
Pittsburgh
Forbes Field (1909-70) - 35,000
Three Rivers Stadium (1970-01) - ~59k (47,952 listed at close, much of the seats being tarped off)
PNC Park (2002-) - 38,496
Cincinnati
Crosley Field (1912-72) - 29,603
Riverfront Stadium (1970-02) - 52,952
Great American Ball Park - 42,271
New York Mets
Shea Stadium 57,333
Citi Field 41,800
St. Louis
Sportsman's Park (1902-66) 30,500
Busch Stadium (1966-05) 57,676
Busch Stadium (2006-) 43,975
There are more examples. I think we're going to see this sort of re-adjustment in hockey. In fact, we already are. The two newest arenas in the NHL both represent increases in size from the buildings they replace, but are both under 18,100 in seats. The Prudential Center at 17,625 seats is the 7th smallest arena in the league. Consol Energy Center at 18,087 is the 10th smallest (having only a handful more seats than arenas in San Jose and Denver).
The smallest arena in the Southeast seats 18,398...which is bigger than every arena in the Pacific division aside from Dallas. Maybe that's part of the issue.