Intriguingly in the Kinetics gallery there's a build where he manged to adjust a rear ti- triangle enough to accomodated an alfine hub, discs might be a stretch. You could have a crazy hybrid to get the power of discs on the front where you want them most
Bang for buck, which set up is best if I was to go down converting my existing Brompton to a disc brake one?
https://www.kinetics-online.co.uk/folding-bikes/brompton/brompton-disc-brakes/