While you certainly cannot migrate the community, I recently learned how comprehensive the import tools are for gitlab. They will import PRs, wikis and a bunch of the metadata from Github and even try to link it all up to Gitlab accounts if the same public e-mail addresses are used by your contributors on the two services. No affiliation, and I don't even use the site today, but I would certainly consider recommending it to open source projects I am involved with in the future.