Dreaming is fun!
My dream is an in-wall with a dedicated fish room on the other side. 6-8 ft tank, 3 feet deep minimum, approx 2 feet tall. 6x3x2 liikely, which comes in around 260 gals. Would stock it with lots of SPS and select LPS as well as some big ass fish like a clown tang, full grown versions of my sailfin and regal tangs, yellow blotch rabbitfish, moorish idol. Throw a couple of schools in there, problably an anthias school and either a chromis or threadfin cardinal school. One rock pillar dedicated to housing an h. magnifica anenome on top, with two other large rock masses placed so that there is a channel of sorts running from the back right to front left of the tank. 500 lbs liverock, whatever I can't fit elegantly into the display will go into the sump. Nice white sand, probably seafloor special, 2-3\" deep.
Inside the fish room, which is ideally about 10x10 feet: I'd run a T5 and MH combo system above the tank. Would utilize a closed loop in the tank to blow water up through the rockwork, and have a surge tank on either side of the display tank that would fill up and dump into the tank in an alternating order in addition to having MP60s inside the tank. There would be a 4x2 foot fragtank along one wall, sitting above the 100-150 gallon sump. Water change station and laundry tub next to that. Dedicated DSB on the other side in a cube tank. Big 5 foot tall external skimmer, chiller that vents outside, a couple of bigass reactors for GFO and pellets, doser and containers for two part.
Maybe a second small in-wall tank that's tied into the main system, sits inside a \"picture frame,\" and serves as a species tank for a peacock mantis. That would be badass.