It doesn't need to completely replace the current platforms. The beauty of the decentralized internet is that platforms suddenly disappearing/dying wouldn't mean we lose years or decades of information that was contained in that site/forum/corporate entity.
Decentralization would also encourage a lot of people to go back to blogging, which would mean information would come from all over the web again.
Instead of learning docker itself, look for a project you really like that offers a docker-based install and deploy that. It'll usually take less than 20 lines of terminal commands. It's a good start that gets you to feel the usefulness of docker, and the basics that you'll need for most deploys.