It has been suggested on the English Meta that questions regarding linguistic topics there should be copied to Linguistics.SE and then closed on EL&U. Now that Linguistics.SE has been launched, what are the plans? How are these tasks normally carried out? Are moderators in charge of this task or is it done on a volunteer base? if so, I can volunteer!
This wont happen too often while in beta. Once the site graduates, there will very likely be a migration path set up, based on need. However, I don't think that one should be concerning themselves about carrying out some massive migration plan so early. Focus your efforts on building this community, and when we've built this one, then we can look at pulling stuff from other communities.
During public beta, it's rather inadvisable migrate too many question into this site. It is much more beneficial generate questions from within the community, than to rely on castoff question from another community. Many of those questions have been asked and answered, and you will not reap the benefits of participation from inheriting those questions here.
Once things get smoothed out, especially post-graduation, it's very likely there will be a migration path setup, based on how many questions may need to be moved. In the meantime, if you feel there is a very strong need to migrate a question, you can flag it for moderator attention.