"Traditional folk is taken as read"

Is it? How about traditional songs and tunes played in modern style and on different instruments? Also, as discussed, many songs and tunes we think of as traditional are not and I'm not just talking about the McTells, McColls and so on.

Anyway, we're talking about "Contemporary Folk" here. To me, this is more than just new songs or tunes writen in the "traditional idiom".

Over the years, contemporary folk might have included everything from Bert Jansch, Incredible String Band, Leonard Cohen etc, folk rock bands such Fairport, Steeleye and so on. Also, whether we like it or not, more modern artists such as Mumford and Sons, some Ed Sheerin songs and so on.
We might not all agree on what is appropriate and the artists themselves may not wish it to considered to called "folk" either of course!

However, I think the test is the music is enjoyed and/or performed by folk artists in general and is "heard" or generally accepted on the folk scene.

Re Richard Thompson's "Vincent Black Lightning", the song is just a bit of fun and not to be taken too seriously. However, it is popular among many folkies and performers such as Dick Gaughan have regularly included it in their sets.
Also many other contemporary songs have been featured in folk artists' repertoires over the years. Lots of Beatles and Rolling Stones songs, for example, and many more"

e.g. Rubee Tuesday Dick Gaughan
    New York Mining Disaster   Martin Carthy
    I don't like Mondays    Dave Burland

The examples are endless. So, there's no reason why some of Ed Sheerin's songs shouldn't take hold in years to come either.

So, in my opinion, it's pointless to argue about what the music SHOULD be. There will always be some cross over and the occasional abberation. As long as we know what to generally expect when we attend a club, concert, singaround or session, that's all that matters.

Like many others here, I find that there is much about the music scene today which I don't like at all but, coversely, there's lot's of great things going on too.
There's actually more choice than ever these days and really no excuse for any of us not to find or do something which suits us. We have to broaden our horizons beyond sixties style folk clubs though.