"Could Ed Sheeran be a good way to introduce traditional Celtic folk music to a new demographic?"

Irrespective of how much anyone here likes the pop singer-songwriter Ed Sheehan, the answer to the OP's questions remains 'no'.

He recorded The Parting Glass - as a bonus track on his first album. That's it. So the most he can be said to have done is introduced some teenagers to The Parting Glass. Everything else he has done is pop with a bit of acoustic guitar, and I think his more recent stuff has gone a bit more soul/hip-hop.

He might well be featuring some Irish dancing in his new video, but the same can also be said of videos from Irish-American hip-hop group House of Pain, Irish middle-of-the-road pop group Boyzone and Irish stadium rockers U2.