I really haven't given this much thought beyond what I did with TXDILAR. I involved the local independent abstractors before they knew they were involved when I listed them. The only criteria I used was the criteria my clients had told me they wanted in an abstractor. They wanted someone who was:

1. Familiar with the local records and indexing systems.
2. Did the work themselves without relying on subcontractors
3. Performed the searches directly from within the four walls of the courthouse

I coudn't guarantee how any of the abstractors on the list did their work but I could create a list of abstractors who were capable of meeting this criteria. So the criteria I set was that each abstractor lived and worked in or near the county where I showed them listed.

So I didn't ask before involving the abstractors but no one has asked to be removed from the list and many learned of the site only when a new client told them this is how they were found. So far, no one has asked to be excluded from the list. :)

So the involvement of the abstractors came because they met the criteria set for the site. The involvement of the lenders, VM's and title companies came because they are looking for abstractors capable of meeting this simple standard.

I don't know if this relates to what you are proposing but it is all the experience I have to draw on. It might be that something like these directories could be used to gather potential members to the LLC you suggest. 

This reminds me of the cooperatives I knew as a child growing up on a small farm in West Texas. The farmers banded together to form a common place to sell their cotton  Before the cooperatives, the big corporate buyers had to find enough farmers to supply their needs. The cooperatives provided a central location where buyers could come to buy cotton in quatities far beyond the capacity of any single small family farm. It worked in the 40's and fifties for the small family farms. Maybe a cooperative would work now to serve the needs of small independent abstractors and their large corporate buyers. It seems to be working with TXDILAR but this is as far as I have taken it.