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This is the 1 bike idea I'm building on for my surly. No where near as seamless as I'm on cable brakes and so they'd need routing and adjusting but that's not too bad. Gears can be sorted by using a dt shifter. You'd need to be fairly careful with hubs though to make sure the rotors are in the same position. A swap over could be done in way under an hour though
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The problem is the stem/reach isn't it? You'd paradoxically need a longer stem on flat bars no?
You can get cable decouplers for your brakes (SJS have some), they're designed for tandems/S&S/Breakaway/whatever frames, then you shouldn't need to reroute the cables.
I wanted to do the same on my road bike to switch between TT/road cockpit.
Though this was pretty neat (sorry, Instagram link). One bike, two wheelsets and two handlebar setups: https://www.instagram.com/rodeolabs/p/BwTAectFIAQ/?utm_source=ig_share_sheet&igshid=81h9icfi6lzy
The hydro couplers are cool and if you are running Di2 or SS it'd be a super quick swap.