Send me an example area that is broken up as you are showing and I will take a look at how to do this best. If you have lines that cross a SI Area and do not set them to Sharp and Texture Boundary then the Texture will flood over the line into the next area. Then if you do a Selection Set of lines, we could likely add an Advanced Select Criteria has Sharp and texture Boundary or Doesnt have Sharp and Texture Boundary and then create a Track Region from those that do have the Texture property.
I am looking at building a tool to texture a surface using triangle shader or sweep triangle shader, or using flood to Texture Boundary or Flood to Breakline to create a SI Area or Texture Area - I dont see that it would be hard to create a boundary around textured areas for example - we do it today as Drapelines in the model - but they will follow all of your boundary lines so they wont solve the issues as is
There is no way to do this today that I know of.
Alan