Currently in the professional broadcast monitor world only about a handful of minitors are available with 4k.
4k projectors are available in many movie theaters.
4k tvs may happen but TV wont be moving to 4k as standard before 2022.
2025 is the time we are looking at for 8k UHDTV in the usa.
Wall-sized screens like in Back to the Future II will be how it goes with 8k.
Yes 4k screens will allow for multiple picture-in-picture viewing also how Marty,Jr. Watched tv in Back to the Future II. 4 1080p HD channels at once.