This is great- Elsevier and Springer (and other for-profit publishers) have been charging exorbitant prices for journals and there have been some other mass resignations where people started a free or at least affordable alternative with pretty much the same board. One of the first big ones was the journal Topology, which reconstituted itself with the exact same editorial board in a non-profit setting, described here. That was in 2006 and though I'd hoped this would spread like wildfire, it has only happened about a dozen times since then.
There are good quality affordable journals, run by professional societies or universities, which are an excellent alternative to Elsevier and other expensive for-profit journals. For the health of science, it is important that people choose to submit there. For untenured people who are under a great deal of pressure to submit to "top journals" it poses a difficult quandary, but for those of us for whom that isn't a concern, I don't see a reason to continue to support journals and publishers which have repeatedly done poorly.
The Cost of Knowledge has lots of information about efforts to improve the scientific publishing culture.
There have been other cases of prominent people are resigning from Elsevier boards; here's a senior researcher in malaria who resigned from an editorial board on the life-sciences side. His motivation was particularly strong- he is working in malaria research, and the idea that people who could benefit from the research may well be not able to pay for the paywall is abhorrent. But I think the same rationale applies to all of science- why keep research from people who cannot pay for it?
In other Elsevier news, more journal shenanigans are described here which include both rigging the reviews to be sock-puppet reviews and getting into their editorial board systems, resulting in yet more retractions. It's not clear what the high prices of journals are paying for when there are intermittent episodes like this.