An Interstate link between Houston and Austin is easy to justify. Hell, the Austin area is big enough and important enough to justify building an Interstate highway West out of Austin by Fredericksburg all the way to I-10. Pretty much all along or near the US-290 corridor. That would be my idea of "I-14" or maybe another "I-12". Regardless of what the route is called, that's the most needed new Interstate corridor in Central Texas.
A lot of US-290 between Houston and Austin has already been upgraded to Interstate standards. US-290 is (slowly) being upgraded more and more heading West out of Austin.
TX-71 from Columbus, TX and I-10 up to Toll-130 in Austin is four laned much of the way with some freeway grade segments in Bastrop, Smithville and La Grange.
Outside of the Killen & Temple area US-190 doesn't have a whole lot of "in progress" upgrades that would develop into a logical East-West Interstate corridor. Between Temple and Huntsville US-190 runs a pretty damned crooked, distance wasting path. It's almost a "W" shape really. There's no need in running "I-14" from Cameron down to Milano and then back up to Hearne and then down to College Station. A new terrain route needs to span from Cameron DIRECT to College Station. Even with that said, "I-14" would be best if it bypassed around the North side of the College Station area and stayed on a new terrain route much of the way to Huntsville. Locking the corridor along US-190 the whole way is just plain stupid. And it might be even more costly to build considering all the businesses and residences built up alongside the highway much of the way.
This I-14 proposal is even harder to justify East of Huntsville, especially if it's just going to dead end at the Sabine River. There's hardly any traffic out there. On top of that TX DOT will have a pretty expensive new bridge to build over Lake Livingston, considering the current US-190 bridge is a smaller 2-lane bridge. Maybe "I-14" could go as far as Livingston and terminate at I-69. Past that there's no point unless it went all the way to Alexandria, LA.
Out west, San Angelo could possibly be a Western terminus for "I-14" if TX DOT could ever get I-27 extended down from Lubbock, through Big Spring, San Angelo and Junction, TX. That route would give the San Antonio region an effective North-South Interstate corridor into the Texas Panhandle, High plains and Rockies. If I-14 couldn't be built that far then it would be easier to turn it Southwest to Junction, TX and I-10.