Participation of multiple researchers in our project We have set up with colleagues in two other institutions a project that creates software prototypes for our discipline. We are creating the software prototypes so that we use them as stepping stones to a larger funding application. The prototype is online and can be accessed via a web browser.

One of the software prototypes is around collaboration. We think we have a good mechanism for collaboration with the potential for larger impact in the industry, but we would need to test it at scale. We think we should invite other researchers to test our prototype, and via testing, we would gain knowledge of its shortcomings and benefits. 

I have looked at other disciplines that organise large collaborative projects and papers with co-authors in large numbers. I and my collaborators are wondering on how to set up the invite to the collaboration. Should we promise potential collaborators a stint in the forthcoming paper? From our perspective, this is the right thing to do, however, our discipline normally does not have mega-collaborations. Still, our prototype has the potential to involve a lot of people. On the other hand, would including them as part of an advisory group be enough?
Do you have any other insights on how and with which mechanisms to invite large groups of researchers to test and (in)validate your prototypes? What kind of intellectual recognition should those researchers receive?
Since professors of CS are often looking for collaborative tools for their students, you might be able to use them as a resource. The ACM has a special interest group for educators, SIGCSE, that maintains a mailing list of members. It frequently gets requests for research participation, so you might try to send a message there, though it requires membership. Other professional organizations may have some similar special interest groups that can be contacted. 

Should you find a huge number of collaborators testers of your collaborative systems I wouldn't think that co-authorship would be necessary in most cases, though you might want a fairly long acknowledgement section in your paper. It would depend, of course, on how much they add to your work.