I think the problem is a bit more elaborate. Mer caters for GPLv3 allergic vendors, but the assumption that all vendors are GPLv3 allergic is worng. Jolla isn't I presume. So, the proper way to do that would be to make two interchangeable subsets of packages within Mer (those won't be all Mer packages, just some which are affected by this issue). I.e. one set for GPLv3 allergic vendors, and other for GPLv3 tolerant. So these sets could be replaceable by installing some corresponding metapackage.

Do you think this can work out? Keeping some packages forever frozen in ancient versions for all users because of the GPLv2 nature sounds a bit weird to me.