He made an appearance with Paul Heaton and Jacqui Abbott so that's probably ticked that one off.
For Acoustic Stage I'd love to see them do a tribute to Sinead O Connor and Shane McGowan
The Staves, Grace Petrie and Katherine Priddy could be a candidate for either stage.
Withered Hand with Kathryn Williams might be a possibility as well. They have an album out and are touring in May.