Sounds like it could be indeed in much of the middle latitudes of the eastern half of the U.S., if what's happening in D.C. this year is reflective.
Increase average winter temperatures by 2-3 in an area that has a mild winter with a great mix of trees and flowers, then have some of them adjust more, and more quickly, to climate change than others. Presto - a four-month "spring" allergy season.
We're talking Washington, Baltimore, Richmond, Cincinnati, Louisville, St. Louis, etc. Any place with a mild winter, lots of both evergreen and deciduous trees, and lots of flowers.
In a place like Texas, it's likely to make less difference, but, who knows for sure? If the central part of the state cycles more rapidly between drier and wetter years, that could affect allergies for sure.