Most likely, you will be able to choose between hiding your activity status from everyone or concealing it only from those selected in the “Who can see my last seen” section.
Although the screenshot was taken from the iOS version of the WhatsApp beta, the new “Who can see when I’m online” feature will most likely come to the Android and Desktop WhatsApp versions as well. However, keep in mind that this option is still under development, and some things might be changed when it is publicly released.
Nevertheless, for quite some time now, many WhatsApp users have wanted an option to choose who can see their activity status. So, it’s great that the people behind WhatsApp have listened and decided to finally introduce such an option to the platform.