I loathe and abhor internal cables. No Singular production frames use them and I have to have my arm twisted to spec custom frames with them. Why is that?
Sure, internal cables, especially the fully hidden inside the bar and stem variety, gives an incredibly nice clean look to a bike. And usually I am all about a nice clean look to a bike. But looks shouldn't come at the expense of practicality, and internal cables have a big fat minus in that column. Doing anything on your bike which involves cables or hoses suddenly becomes 10 times more difficult. Particularly if you're the sort of person who often swaps parts between bikes, or wants to switch around their component configuration, internal cables are just an enormous pain in the arse. Magnets, zipties, string and vacuum cleaners become part of the bike mechanics arsenal - that and a whole new lexicon of invented profanity to adequately express the frustrations of trying to get a cable through a particularly recalcitrant fork. Then there are the mystery rattles and creaks which are impossible to track down, let alone silence.
But external cables, especially full length outer ones that just bolt on to the outside of the frame like Singular's do, are just so simple to work on. Fitting a new gear cable is a five minute job - not an extended battle, fishing cables through a frame, sometimes taking the bike half apart.
External cables also provide great flexibility of cable routing for choice of which hand operates which brake while still allowing a smooth cable run. Or if you want to swap out bars, brakes, gears, etc you just unbolt, take them off and put a new one on. If travelling and needing to box up your bike you can easily just completely detach bars and fork for simple packing.
So far as I can see, all production Singular frames will continue to be all external cables only - optimised for mechanical gears, but that's another blog...
Sam