The Virtual Researchers on Call program looks really cool! I can imagine different scenarios (especially as a teacher to primarily seniors in high school) that a program like that could be extremely useful. Is this used mostly for teacher-expert interactions, or do the experts directly interact with the K-12 students?
I believe that the experts need to be both experts in their STEM fields, but also experienced teachers. There are many people I know in the scientific community that are extremely intelligent in their subject, but are not able to disseminate information effectively to teenagers or do not have classroom management tools or techniques to be the most effective partners. We envisioned teachers with >/= 5 years of experience (at least) of teaching a specific subject at AP level. These teachers would have a specific region or district(s) within which they functioned, and would interact with all of the teachers within that region or district(s) that taught the particular subject. The expert teacher could respond to teacher requests and/or decide to focus their attention on select teachers due to performance reviews and/or observations.
My colleagues and I discussed that our direct supervisors often do not have content-area knowledge and therefore cannot offer the most useful critique/suggestions and professional development. In our minds, expert teachers would be able to not only coach, but guest lecture in the classrooms of struggling teachers - this could include working virtually with a kit, as you suggested.
In our network, teacher turnover is relatively high and new teachers are easily overwhelmed with all of the requirements on top of teaching a content area. We feel that expert teachers would offer the most useful professional development and therefore increase the chances of staff longevity.