well, lets keep it within reason, to the extent you cant add sme gyro tourbillions..etc.. but just say you could design a dream piece that you would love and wear as a daily... forever.
ill start off as the first,
my dream JLC would include my favorite case design out of any watch made, the reverso squadra case (large size from the worldtime squadra) but in steel rather than the TI the worldtime comes in.
the movement i would choose basically the movement out of the "reverso grande sun/moon" (hopefully slightly larger to fill the case as well as to include two more functions which is: a double date, and the "hometime" extra hour hand found on the "squadra hometime" by far i feel that the double hour hand is the best way to create a "hometime" watch as its the easiest to read (i hate 24hr hands). the "sun/moon" movement of course would be an 8 day manual wind movement, sun rise/set complication, moon rise/set complication, power reserve, small seconds, and display back.
the extras of course would need to be squeezed into the setup, the hands would need to be larger and i would allow them to remain blue like their "older brother" hiding a hallow steel hand under the blue hour hand for the "hometime" .. the AM/PM indicator wouldnt be needed for the hometime hand because i would have the sun/moon complication be always tied in with the hometime hour hand. the date however would change forward/back with the "current" blue hour hand. (not sure if even possible to move back the double date JLC uses). the double date would be placed in the upper left where the reserve is now and reserve relocated to the back similar to the limited edition grande Dates..

a poor rendition i made of my dream piece, and given its basically a grande sun/moon with date and hometime i feel it would more than likely be priced around ~13,500.00 USD or so, on a blue croco of course w/ double deploy.
riley