Internally routing or Hiding Di2

yes. maybe a bayonet fork or front fairing is a better idea.

Front brake hose in front of headtube under fairing.
rear stuff on top of stem (under a cover) into a top tube that is slightly higher

Inspiration:

(just the shapes , not the actual brake setup)

or extend the headtube (with a extra tube :)) like this:

https://cyclingtips.com/2019/12/bikes-of-the-bunch-stinner-aero-camino/

just ehhmm... neater than these examples :)