I honestly like the idea of Interstate 14, and I'm open to different routing ideas. This may start to dive into fictional highway territory, but this is what I think could potentially be a good idea:
http://prntscr.com/dsfdic - have an Austin-Houston corridor consisting of I-14 and I-214, in which I-14 may connect to I-10 southwest of Fredericksburg - I-14 goes east from Austin to the Houston Metro Area, but it veers northeast onto the alignment of TX 99 (so long as it is up to interstate standards), with an Interstate 214 3di designation continuing on the alignment of US 290 into Houston. Also, I-14 is briefly concurrent with I-35 in downtown Austin. This serves the need for an interstate-standard corridor from Houston to Austin (both of which are up in the realm of the nation's largest cities), while I-14 traverses the northernmost suburbs, then becomes concurrent with I-69, then splits off east again for Louisiana to eventually tie in with its proposed route over there (and with that going on, and its proximity to I-10, perhaps have an I-x14 connect I-14 & I-10 in Beaumont). It sounds like it wouldn't
hurt to have those military bases on the interstate system. This is where Interstate 18 can come in. Perhaps an I-18 corridor can take the designation of the US 190 freeway near Killeen and Temple. Going west, I-18 could eventually serve San Angelo, then eventually connect to I-10. I-18 could be concurrent with I-35 up to Waco, then an Interstate 18 corridor could suit the need for an interstate-standard corridor connecting Waco, College Station, and the Houston Metro Area. I could have the completely wrong idea, but I have tried to find a solution that satisfies as many of the insights I've read in this thread as possible. For US 190 near Fort Hood, a I-x35 interstate designation could also work out fine. Also, if the I-14 gets built as congressionally designated, it would at least be a placeholder in anticipation of growth throughout the region, as someone said earlier in this thread.
However they're routed, I think Texas would do very fine with a new I-14 corridor and a new I-18 corridor - and in addition to that as well, the talked-about I-27 extension (both ways). I think San Angelo could do well with Interstate 18 for an east-west interstate, and Interstate 27 for a north-south interstate. It
also wouldn't hurt to extend I-44 to Abilene, or even to San Angelo.
In short, I think Interstate 14 sounds like an exciting idea, and I hope it is not too long until it is built, including in Texas.
EDIT: In that map, I meant to keep the red line of Interstate 214 going until reaching I-610, not stopping at TX 8.