There is simply no way that the GOP members of the Texas delegation is going to vote for this amendment. Cornyn and Carnival Cruz will filibuster this amendment and I doubt that there are 60 votes to approve this amendment. I agree with Drum's assessment that the GOP has given up on getting minority votes for the foreseeable future
This may change if Texas is "bailed in" to pre-clearance under Section 3 of the VRA due to either the voter id or the redistricting lawsuits. If Texas has nothing to lose, the Texas delegation will not have a motivation to block this amendment. In addition, seeing some states being "bailed in" may encourage some other red states to vote for this amendment. The Texas voter id lawsuit goes to trial on September 2, 2014 and in the next couple of weeks we should be getting a decision in the Section 2 case dealing with the Wisconsin voter id law. A victory in either of these two cases combined with the ruling in the PA voter id case may put some pressure on the GOP to consider this amendment