Couldn't it be said that there was a third revival (at least, in England) in the late sixties/seventies starting off folk/rock (Steeleye Span/Fairport Convention/Albion Band...) and moving more acoustic (Old Swan Band, Blowzabella...) before we entered the Dark Ages of the eighties and early nineties?

Similar things going on in Ireland (De Dannan, Planxty...) and Scotland (Battlefield Band, Ossian...).

Largely instrumental, as now, and very different from what was going on in the fifties.