I already use a 4K TV for a monitor. 8K would just push a need for a more expensive video card, while decreasing how well people can see when I share my screen. Even on a 4K, I need to blow it up to ridiculous zoom levels to make a screen-share readable to others.
I'm sure not everyone would run into that problem, but it is a fairly strong con to be aware of.
If you are on Linux, you can divide the entire screen into multiple virtual monitors and share only one of them. This has the benefit of giving you "private" monitors what won't be shared.
Another option could be to temporarily lower the resolution.
I'm sure not everyone would run into that problem, but it is a fairly strong con to be aware of.