The pros often hide them in a closet behind the wall. Do you have one?

This sounds like a problem that he needs to figure out, because he's the one who drew that line in the sand.

At any rate, it's not a Design Dilemma, it's just an electronics problem.

I did a rack in the basement that housed all the gear. I controlled it with an IR repeater system. Very clean look

There are many wireless systems so he better go shopping . Myself i find the cansole under the TV not only useful but attractive andholds so many other things like the kids games etc. along with the fact it hides the wires they just make sense. Ikea has a system called Besta that you can make look custom and with size TV you will need to go that route or custom.These are just a couple of ideas. Please make sure the TV is also hung at the proper height , the center of the screen needs to beat eye level when you are seated

Where are your speakers going? Are you going to have an AV receiver? In my first media room (which was in my attic), I mounted the TV on the wall, put a small table below and to the right of the TV on which I stacked all the other devices: AV receiver, cable box, DVD player, BluRay player and SACD player. The center speaker was below the TV and the four other surround sound speakers were in their appropriate places.

In my vacation home, I (so far) have dispensed with the AV receiver and surround sound. I have the TV on the wall, a small (40" x 4" x 4") soundbar under the TV, and all the other components stacked on a table on the other side of the room. 3 HDMI cable run to the TV and all the source selection is done using the TV remote. I may eventually run the HDMI cables inside the wall, but for now, they run along the baseboard. The soundbar (with wireless sub-woofer) sounds surprisingly good, so I may never upgrade!

there are brackets that hold various tv boxes on the back of the tv. Speakers can be mounted to the wall with brackets or set on stands.

Another idea is to consider eliminating components. Blu rays can be "ripped" to a plex server located in an infrastructure area.