It's not really that odd or unprecedented to close an older structure or hotel for a few years and totally re do the infrastructure. It's a beautiful historical building but was not built with the technology of the 20th Century and what will come in the 21st Century.
Im sure dating into the 19th century, electric lines were installed, lighting fixtures placed or even back in the 40s or earlier, thick telephone lines were installed, then came TV
sets, wall mounted sets, A/C, or whatever convenience was necessary for a discerning clientele. The building probably took a beating over the last 100 years in being converted to new technologies that it was never built to house.
There are pix of the White House being completely restored in the 30s because the floors and support beams were in danger of falling apart due to constantly being upgraded with the times since the 1790s. The literally removed all the mouldings, fixtures, historic walls and stored them and rebuilt the support columns and replaced the wooden support areas with stronger materials. Then placed all the fixtures, mouldings , walls back to their original areas But even things like bathtubs, you dont realize how much weight they cause to a buidling and who knows if the Ritz was built with bathtubs in mind. Showers probably not in its early days. So, the grand dame has definitely taken a beating over the years and will re open completely modernized and hopefully historically intact.
On a side note, I used to work in a trading environment in San Francisco in the 1990s, and the Bank of America building was built in the late 60s and when the trading floor was initially built, they had to raise the floor a few feet to handle the sheer amount of cables to support a 200 person trading group (foreign exchange, derivatives, bond trading etc) and their old computers of the days, telerates, reuters machines, then faxes, printers etc etc. So they needed that two feet to put all those cables under the floor. When they decided to re do the floor in 1997, they decided to just simply start anew and built a new one in another building built to handle that. Obviously that's not possible with the Ritz in Paris...