This really does seem like a very sensible way forward.
The pod-style seat used on planes is very well developed and I've been fortunate enough to fly in the expensive seats a few times. There are a number of different types but all of them offer comfort, entertainment and decent sleep.
They are effectively off the shelf components and are easy to source competitively - a nice way to get a good price. It really wouldn't matter what they were installed into. It could be a MK3 shell, a new IEP body shell or anything else without 1/3 & 2/3 doors. I really do see this as a way to get a cost effective sleeper system without the need for vast capital costs.
Of course, such pods are usable as seats. This would allow a far better utilisation of stock. A diagram could be:
Glasgow (late pm) to London (early am)
London (9am) to Manchester / Liverpool / Birmingham as a luxury service
& the return working
London 5pm again to one of the other cities
London (late pm) to Glasgow
(And of course there's the opportunity for some daytime services within Scotland)
This seems to be a far better use of the stock than having it sat unused between 9am and 10pm.
There's the business model - anyone got a few £million to back my tender for the service?

Jason