A guild license is a way to deal with content shared among a specific group of people, possibly those who use it in their work as a method or tool, and who do not make it publicly available to everyone. It would apply quite specific conditions including potentially a mutual nondisclosure agreement and non-compete agreement for certain uses.
It would be Share Alike only to a small group of participants - unknown participants would be effectively excluded since what such participant commits to group use isn't of any use or value if they don't already have access to the guild knowledge base or tools.
It would be a parametric license so it could enable a rights market between the guild-certified participants, who would not have to meet each other or ask permission or negotiate anything except the price to apply a certain tool or method to a certain job on a one-time basis. All other terms would be defined clearly in the guild license itself.
Such licenses might make it much easier to form lateral associations of craftspeople who all had a common commitment to a single code of ethics or professional best practices regime. This might allow for much more rapid creative network formation, though it would not increase the public's access to the guild's closely-held educational content, which would be kept for the exclusive use of those who adhered to the ethics and practices, as in most professions.
Such a license increases Common Content by letting any small group create its own detailed restrictions or conditions that are satisfied by some method regulated by itself, but without any need to ask direct permission of others who agree to the same terms and have the same certifications and mutual agreements to ensure a certain high quality of output or to restrict access to certain dangerous tools to ethical persons.
Such a group gains the benefits of a small amount of Common Content they create amongst themselves but retain the power to withdraw it if someone acts against the ethics and interests of the whole industry. This model is basically a more open kind of corporation or union but that commits to CC-like terms only among "its own people" as long as they are in compliance. Such an option could bring in lots of groups of influence including perhaps the Writers Guild of America or Certified Linux Professionals and so on.
An interesting possibility is that if the group or guild disbands or if it goes bankrupt, an escrow agreement applies so that all of its work can be placed under license that allows the work itself to continue under compatible values, e.g. GPL, CC-by-sa, CC-by-nc-sa, peace license or green license, that would continue to reflect the group's values (sharing only, sharing among those who do not profit from it, peace, non-extinction) even if the group itself no longer exists - and thus no longer has interests nor any capacity to project its code of ethics in any other way than its choice of default license.