@offray.luna dual licensing is one way to address this. i didnt recommend it because if you dual license cc by and afl, it (usually) has the weaknesses of both-- this is most relevant to your concerns about copyleft.
i also technically suggested two licenses, but not for the same work-- i wouldnt call this “dual licensing” because its really single licensing for two different purposes and two different works.
license proliferation mostly comes from misunderstandings about existing licenses, or an organisation wishing to push something in a different direction-- not always through a need. occasionally of course, there is a true need for a new license. i would stress scepticism towards any such need, but they do sometimes arise.
imo, people are prone to trying to make “licensing” do things that could be done by other means. with your concerns about copyleft however, the only real solution (within the existing oer paradigm, that is) is probably to use copyleft for source code, and cc by when appropriate to your needs.
to me, this is not about whether cc by is “enough” for oer, but whether your source code really falls under the “oer” umbrella. what youre looking for (ive looked at your site) is free software licensing. but thats no reason to not participate in oer when the shoe fits.
its not that i think oer licensing suits every community. the lines between free software, open source, and free culture (somewhere in there, oer) are more pronounced than ever. i do think cc by suits the oer community-- and i am interested in detailed arguments (from anybody with the time or interest in making them) why cc by would not suit oer-- this opinion isnt set in stone.
but i think your hackerspace is probably leaning more towards other aspects of free software/free culture, and while im glad that oer is trying to stand against license proliferation, i have to note that free software and free culture use variety of licenses, one of which is likely to address your needs (or even adopt the afl.) http://freedomdefined.org/Licenses
please note that i think the hackerspace is a good idea, i applaud and encourage your use of free licenses, and im (always) interested in the place where these different efforts meet together. if you are concerned about copyleft, perhaps leaning towards afl is the right decision for your group. if the group produces more free software than textbooks, why the stress on compliance with de-facto oer standards?
unless im wrong, and your group is focused on producing non-software educational materials, but thats not what i would expect of a hackerspace (i wouldnt preclude such a hackerspace, ive simply never heard of one like that.)
please note these are opinions intended to be (sincerely) helpful, and i appreciate if instead it comes off as being exclusive or dismissive-- thats not the intention. the intention is more like if someone said to me “this coat is too warm for this time of year” and i said to them “can you tell me why youre not wearing a jacket instead?”
i try to learn from everyone, and i assure you this is not one-way advice. i will probably be giving your post some thought all week long. hackerspaces are the best, i wish you the best of luck with yours.
an additional note: although im quite fond of opencontent.org, it is a now-defunct organisation that has ceded its goals to creative commons-- and been succeeded by open knowledge foundation, and definition of free cultural works.
generally speaking, i think oer is on the right path.
specifically to the opencontent.org efforts to introduce copyleft to non-software, i think a very strong case needs to be made for it. the really big problem with copyleft for non-software that cc by (and oer) neatly avoids, is the difficulty in navigating the requirements that results in lower participation in the production of oer works.
if a more permissive license results in significantly greater participation, then copyleft is not what oer wants. but for your software, there are great arguments to be made.
until a stronger case is made for copyleft of non-software, its probably going to have few proponents (and fewer participants.)
in a collaboration, a license that allows many more people to particpate is also subject to network effects. diversity is something you want with participants-- but not with licensing.
“diversity in licensing” means exclusivity in participation, and making participation more exclusive (fewer people can or will reuse the work) requires a really good reason, to go with the higher cost. considering the headway oer is making, the reason needs to be something that happens “in practice.” i suspect that the reason david wiley gave up on open content, is that he decided it was an alternative to something that was truly working well enough-- but i only assume this.
i believe the founder of opencontent.org now works at or even leads lumenlearning.