while I would say I belong to the dark-theme cult, there are some applications/websites that I cannot get used to them in dark mode. Like github or slack for example in which everything else than they light theme looks strange in my eyes.
meta (threads) will not support fediverse already. They said they will do in some later version. So for the completely practical part, you don’t need to do anything right now.
meta is not here to promote open networks. They will do more harm than good. If you want to learn more about how google achieved it with the XMPP you can read the story here https://ploum.net/2023-06-23-how-to-kill-decentralised-networks.html written by one of the core developers.
large companies and influential people are in the commercial platforms because of the ads. There is literally no reason for them to move in a place without ads.