Why stop at CC-BY on the road to freedom?
Recall that the rationale for using cc-by-sa includes growing the commons and encouraging a culture of collaboration and sharing (share and share alike). It is tactical.
With cc-by the resources may be adapted (or not) and incorporated into 'all rights reserved' mixes and sold - an incentive to those who just want to make money out of other people's work and impose restrictions.
Having one license cc-by-sa across all resources makes it easy for people to mix without having to think too much. For example, it is easy to copy/paste/adapt (mix) text from multiple WikiEducator/Wikipedia pages - but easy to miss a potentially incompatible difference in licensing (e.g. if WikiEducator also includes cc-by text).
It is possible that
(1) The share-alike tactic is unnecessary. Successful examples include PLOS, Connexions, ..., and as far as I know, no-one has demonstrated that the tactic works (except possibly Wikpedia) or can explain why the tactic nolonger applies for WikiEducator (it does still apply for libre software).
(2) the (WikiEducator/...) user base is sophisticated enough to handle such license issues (and not mix cc-by-sa content from WikiEducator/Wikipedia etc. into cc-by resources on WE/cnx/...).
If both (1) and (2) apply (i.e. share-alike is nolonger a necessary tactic for growing the WikiEducator commons and our users, including new future users, are savvy enough wrt licensing), then why stop at cc-by on the road to freedom?
By doing so, copyright law is still being used to 'control' an aspect of human behaviour which in my opinion should be cultural.
Why not focus on CC0? The existing culture in academia will ensure attribution. The the resources for open content licensing project's intended guidelines could cover such cultural norms.
Technically, it is difficult to check if users mix cc-by-sa text content into cc-by resources (or cc0 resources).
For some time there have been tools and services available to catch plagiarists (e.g. Turnitin), and I have long wondered why these are not used in a positive way (tools to help learners/writers etc. to be more original, recall and reference sources and improve their writing). Such tools do exist now (e.g. http://www.grammarly.com/ ) and even Turnitin is marketing itself as preventative: "Prevent plagiarism. Engage students.".
It would be great to find/develop libre software alternatives (on account of costs, privacy issues, etc. - see for example: http://researchforward.wordpress.com/2007/03/29/should-faculty-turnitin/ ) - as tools to assist authors.
So, perhaps we are becoming more enlightened, and cc0 would be the way to go now? http://wiki.creativecommons.org/CC0_FAQ
On WikiEducator, permitting cc0 content could also mean relaxing the requirement to login to edit (as does Wikipedia).