Here are the CAMPO 2045 arterial plans. Looks like they anticipate (or propose) that both 71 East and 290 East will be limited access, at last in the outer metro area:
https://drive.google.com/file/d/1hJvCstSua55osbz013HvPSKzf7Pw7G6b/view?usp=sharing
Nice to see both US-290 and SH-71 as limited access heading east... unfortunately US-290 to the west ends limited access at Dripping Springs. For a true long range plan, should extend out to US-281 at a minimum, or in this case, to the edge of the metropolitan planning area.
If US 290 we’re to be upgraded to limited access from Austin to Houston, I could see it become an interstate, as least to connect Houston to Austin. It could be a new designation, or Maybe it could be a continuation of I-12, (could be co-signed with I-10 from Houston (I-610 interchange) to Baton Rouge (western terminus), like 20/59 from MS to AL). Not saying it will become interstate though, but if it did indeed become one, would it still be cosigned with I-35 in Austin?
Unless it continued on west back to I-10, a multiplex with I-35 would be pointless; it would likely just end at its junction with that route. Since we've let a bit of Fictional through the door -- it would likely be an independent western I-12; signage from Baton Rouge to Houston would be a bit gratuitous.
Also, the Bergstrom Expressway just opened east of Austin, on which the designation could run…since it connects to 71 west. Versus dumping traffic on an already congested I-35.
This is why I have pushed for SH-71 east of Austin and US 290 west of Austin as the preferred El Paso-Austin-Houston interstate. Many reasons.
-It's a straight shot through Austin without a co-sign.
-It would relive any cross Texas/cross country I-10 traffic from dipping way south to San Antonio.
-It would effectively act as the I-35E and I-35W split being the 71/290 version being more of an I-10N and the existing I-10 from Columbus to Segovia being effectively I-10S
-It would be relatively less work for a greater impact. Not only would the upgrades be minimum, especially through Austin and east of Austin, but it is a 220 mile corridor to upgrade to make an impact on a 2,500 mile corridor. Just 220 miles to make a coast to coast interstate.
-Finally the El Paso-Austin-Houston corridor will be connected by interstate.