Just curious, what is the worry about compatibility between bikes? If you use 11 speed compatible freehubs on both, you can share wheels easily enough with a cassette swap. What else are you looking to share? Maybe cassettes, which I kinda get but those aren't all that expensive especially for 10 speed ones. 10 to 11 speed drivetrains really aren't that big of a change. I doubt you'll miss it if you appreciate riding vintage feel. That feeling will overwhelm any shortcomings in the groupset in my experience. My vintage steel Trek has 11 speed 105 vs. 11 speed Campy Chorus (my preferred ergonomics) on my main road bike and I still enjoy riding the Trek.