What gives? It seems like almost every state has a National Scenic Trail except Texas. Maybe they're saving the best for last.
With the almost total lack of any kind of public land outside the postage-stamp-size state parks (BB Ranch the notable exception), BIBE/GUMO, and the 4 national forests in the east, good luck on seeing any kind of long-distance trail being created between such features.
Not that it couldn't be done, but Texas does not have much of a land access ethic, unless you count buying hunting leases, since it is predominantly privately owned. Even if landowners were receptive to the idea of allowing a trail across their lands, the negotiations over access and compensation would take years, not to mention actually establishing something on the ground.
It would be an admirable goal for some organization like the Sierra Club to pursue, but they probably aren't exactly welcomed by a lot of the large private land owners. The Nature Conservancy might have a better go of it, since they tend to put their money on the ground rather than in politics.