Ask Mr. Smarty Plants

This sounds like a very interesting project. Mr. Smarty Plants recently visited Avignon, France where a wall of their Halles (market) building is covered with living green plants. Beautiful!

The vines you suggested certainly should work well planted at the base of the wall growing up, but there isn't any reason that they wouldn't also look nice if they were planted near the top to fall down the wall. Mr. SP also thinks the Muhlenbergia reverchonii (seep muhly) would work; but, rather than ferns endemic to Enchanted Rock which would be difficult to obtain commercially, why not consider sedges (Carex spp.) such as Carex cherokeensis (Cherokee sedge), Carex perdentata (sand sedge), or Carex planostachys (cedar sedge). More grasses or grass-like plants that are possibilities are Eragrostis intermedia (plains lovegrass) and Nolina texana (Texas sacahuista).

You are going to have to take into consideration whether the plants are going to be in part shade or full sun. I suspect most will be in full sun. Here are some possibilities arranged by that feature:

Part shade

Aquilegia canadensis (red columbine). These are often found growing in dirt filled depressions on the tops or sides of honeycomb limestone.

Clematis pitcheri (bluebill). Vine.

Lonicera sempervirens (trumpet honeysuckle). Vine. Semi-evergreen.

Sun

Bignonia capreolata (crossvine). This will also grow in the shade, but will not have as many blossoms in the shade. Vine.

Campsis radicans (trumpet creeper). Vine.

Lonicera albiflora (western white honeysuckle). Woody vine or shrub that will also grow in part shade.

Lantana urticoides (Texas lantana). Another name for this plant is "trailing lantana."

Muhlenbergia reverchonii

Carex cherokeensis

Eragrostis intermedia

Nolina texana

Aquilegia canadensis

Clematis pitcheri

Lonicera sempervirens

Bignonia capreolata

Campsis radicans

Lonicera albiflora

Lantana urticoides