About the only clean way to remove the internal routing would be to remove the cap and fill the hole with brass and file it to the tube contour. So yes pretty much change the top tube or make another frame and be sure you end up with a frame where you want to keep the routing internal.

I would like to go for external routing because I want to make a rinko bike of my actual bike.
External routing allow you to remove handlebars without untighten rear brake cable.
Any other solution is welcome.

I do travel and often take train or small cars with friends of mine.

Are your tubes round? The easiest and reversible way to go external is with clamp on cable stops. Andy

Yes they are but it would looks awfull.
Does any know a brake quick release with housing ?

All the rinko bikes I have seen have the rear brake attached when they are rinko'ed

Some calipers/anchor bolts do less damage and are easier to fully disconnect then others are. Whether these are applicable to your bike who knows. Andy

If you have a budget of $1000-1200 you could convert to Shimano Di2, one wire to disconnect the handlebars from the derailleurs. Use SW-R600 Remote Climbing Shifters instead of brifters. Look for a set of Sram hydro disc levers with the inline coupler to disconnect the brake lines near the handle bars, this is found on factory installs and occasionally comes up on ebay. The coupler seals when taken apart and from my understanding is good for 7 or so disconnects before a bleeding is needed. Shimano has couplers but they do not seal. I don't know if the sram hose will fit a shimano hydro brake assy. Unfortunately the female part of the coupler is not available retail.

There are rumors of other companies making after market couplers but so far I am unaware of one in production.

Just another solution

Good luck with the conversion.

After a quick google search Sram may have come out with the couplerSRAM HYDRAULIC BRAKE HOSE WITH Connectamajig Connector 1350mm

Thank's for your interest I might create another post to see if any solution.

I have no interest in internal cables (too many compromises for no real gain) but keep coming back to this thread.
has anyone ever tried incorporating cable entry and exit points into the lugs? An extra lug point on the side of the tube with a suitable shaped window for cable entry. Would this be less prone to failure?

Trek had their internal routing ports incorporated into the castings. In fact the internal shaping of the castings were conical in that they guided the bare cable to the exit port. I have seen bikes with oval top tubes that had the ports at the major axis "ends" as they stuck out past the narrower ST and HT. Port reinforcements to mitigate thin wall cracking is a common element on many versions. However incorporating (love that word...) this reinforcement into the lug isn't very common. How the casing loops are routed or their "size" would be a concern of mine since I ride a small size bike and don't like tightly curved casings. Andy