Wizards just announced D&D 5e basic which will be a free pdf. Should this be a seperate tag?
Not in advance, tags are emergent
Probably not. Look, we have some versioned tags, mainly for D&D, to reduce confusion, but there is such a thing as too much differentiation there. We don't have separate tags for Essentials, for playtests, for beginner boxes, etc. Normal games get away with a tag for the game, and ask in your question text if you really need it more precise. D&D gets big version buckets, but these really are intended to be "you know, the version of D&D published in a given decade" and not a tagging system designed to mimic the company's specific release schedule. Major version is as far as tags do - or IMO should - go.