My Brompton is from 2012, that's now almost 14 years, no Deltec cable and no maintenance required on the hinge. The hinge of a tri-fold is not located at the same place as on a bi-fold and the constraints on it are different.

The IGH of the G-line is a standard Shimano IGH, any Shimano reseller should be able to do the maintenance if the bike owner cannot do it (its not difficult to do, its just annoying). BTW. if I understand well, Dahon use the same on the 20" Lunden?

But, I also do not like this IGH, gear inch range is too limited and its heavy. Brompton should at least have mounted the Alfine 11 (which is also easier for the maintenance).