Will the Democrats be able to pit the Establishment Republicans and the Tea Partiers against one another the way the Republicans used to do with the liberal and conservative Democrats?
Well the idea is to run an Ed Brooke like republican and convince him to switch to the democrats and run for the senate. . He could then make the case that he shares your values and being a former republican, could win over some republican votes. The only problem is that a lot of Ed Brooke types in Texas are probably already democrats.
The closest Texas ever had to an Ed Brooke Republican in elected office was George H. W. Bush as a Houston congressman in the 1960s. They ran quite a few Republicans who were arguably to the left of their Democratic opponents at that time, but none of them won. In 1968 and 1970, Paul Eggers ran for governor and made a higher state minimum wage part of his platform. And Ray Hutchison (state legislator in the '70s; husband of Senator KBH) was the only Texas Republican I can think of who was unequivocally pro-choice.
Texas doesn't really have much of a moderate Republican base, with the exception of certain upscale neighborhoods in Dallas and Houston, and some Texas Germans in the Hill Country who vote more like Midwestern Republicans than Southern ones.