OK, despite the fact that the whole concept of the ultimate build, bike, gruppo, or whatever is kind of ludicrous, and in my view we get way too wrapped up in the bike rather than the tour...

My perfect gruppo would probably be something that combines the simplicity and the functionality of my old down tube shifter, 1990, 105 gruppo with a 10 speed cassette and probably a double ring in the front. That or an equally functional STI brifter system, but with either non indexed front shifter or a trim adjustment. Since I travel light there is no need for wide rims and tires, so the dual pivot 105 road brakes work wonderfully. No need for a lot of bells and whistles.

One of the problems for me would be that the newer frames are often not made to accommodate down tube shifters so the DT version might not work easily for many frames (btw, I strongly dislike bar end shifters so they are not the answer for me).

A lot of the two ring, 10 cog MTB drive trains would suit me fine with a set of either DT shifters or brifters (assuming they worked properly with the MTB drive train) and some road race brakes.

Truth be told my 1990, 105, 7 speed, short cage, downtube shifter, road race gruppo with a triple crank converted to an ultra compact double already comes pretty close to being my ideal. If anything a few more and closer spaced cogs would be nice. I would never have guessed how much I would have enjoyed that setup when I threw it together to do the ST with U/L camping/cooking gear. The 1990 Cannondale Crit frame even comes fairly close to being my perfect choice.