If you’re relatively close and interested in a long rail trails, I’d recommend checking out the Katy Trail next door in Missouri. It’s the longest rail trail in the US.
I wanted to call bs on this, but for now it seems you are right. In Texas, there are plans to take an abandoned railroad line from about Farmersville to a location fairly close to Texarkana. I am not sure the exact mileage, but I would think it must compete. Here is an off the cusp link about it.
It only manages to pull off this designation because the route from Pittsburgh to DC is technically 2 rail-trails (there's a tiny road segment of less than a mile that connects them in Cumberland, MD). Either way, the more rail-trails the better!