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I don't think I'd be bothered about internal routing although internal routing for the hydro could actually work as I'd be using the actual caliper as the junction so possibly could go internal as far as back half and then surface mount on rear triangle?
I don't want to get too carried away though as I'm trying to keep the cost in line and same for the paint!
Nahguavkire-
Depends on whether you'll be needing to detach the handlebars for packing, if the hydro cable goes through the frame, then its going to be a bit awkward?
I was actually talking about the di2 wires, as it's ugly to mount them externally and the complication of having a seatpost battery that you'd need to detach for breaking down the frame.
Rival/Force 1 cable with cable discs or hydro would seem like the most practical option.
e.g:
https://www.ebay.co.uk/itm/sram-force-1x-gxp-groupset/142748967771?hash=item213c80635b:g:KyUAAOSwAy5avlcM
Acliff
If you go cable shifting, the Ritchey quick connectors work really well, and with 1x you would only need the one.
Internal routing with a breakaway frame would be a bit of a faff, unless you put a junction box near the splitting part of the down tube?