It’s important to use services with a workflow that works for you; not every popular service is going to be a good fit for everyone. Find your balance between exhaustive categorization and meaningless pile of data, and make sure you’re getting more out than you’re putting in. If you do decide that an extensive amount of effort is worth it, make sure that the service in question is able to export your data in a data-rich format so that you won’t have to do it all again if you decide to move to a different tool.
I’m not sure how much actual effort it takes to make sure Plasma keeps compiling for X11, but based on the wording from the blog post it sounds like they’re exerting pretty much as little effort as possible. I would say with the recent uptick in leading-edge distros moving to Wayland it’s only a matter of time before almost no one is left on X11, which will deprioritize it even further. Pulling the plug on X11 today is premature given how many people are still running it (SteamOS uses it by default, for example), but I think their ~2 year estimate sounds about right for letting off the gas and putting a hard stop on support.