I would say "renewal of interest in..." rather than revival after all there is no need to revive something which is in a perfectly healthy state.
I see the Billy Bragg's of this world as bridgebuilders rather than invaders (arguably the people who participate in the likes of "Rubber Folk" are reciprocating.)
Once you have a bridge you can cross back & forth at will.
There must be many people who have had their interest in Folk ignited by a folk-influenced rock act/song.
I hope they will be always welcomed.