I've read about features being shuffled off into plugins instead of keeping them as part of the main WordPress (core files) which can be downloaded and installed for free (web hosting/ domain required). The problem with features being taken out of WordPress is where they go from there.
Premium versus Free
WordPress itself is still free. Plugins are less often free these days. There could be a free version, a limited version, and in a few cases just a pretty free face advertising the premium plugin. This is what I see happening to any features taken out of WordPress and left to develop as plugins instead. Wave good-bye to your features.
I do understand plugin developers want to be paid too. I have paid for plugins and usually lived to regret it. Paid plugins need to be supported. This does not mean people need to keep buying them, keeping the developer happy with a lot of sales. No, once I buy a plugin (or other software) I like to know it will be supported (if not actively developed it should at least continue to work). Paying for a plugin does not guarantee it will be there, functional, when you want it.
Features in WordPress core tend to be more reliable that way.
Another problem with plugins is discovering they are not what you expected and then trying several others hoping to find that one magic plugin that does the job. All plugins are not created equal. They conflict with other plugins and, they don't always work smoothly with your site theme. Trying several plugins is risky, all that installing, activating and deleting leaves a load of junk on the back end of your site. You don't see it, but it's there, lurking, a possible conflict of interest when you least expect it.
Features in WordPress core are far more likely to keep evolving and getting better than features taken out of it. That is just simple logic.
Look at post formats. They were taken out of WordPress and have been left as an empty little icon you can add to your posts, signifying nothing really because you can't add style to the post formatting unless you modify the CSS/ HTML of your site files. Not everyone wants to do that. So post formatting is kind of a dead fish. It could be a better solution than page building plugins. It could have meant we did not need page building plugins.
Instead, page building plugins have evolved and page formatting has stalled out somewhere along the way. Formatting would have been less complicated, more user friendly. But, WordPress is run by developers who sell plugins. There is that bias towards being commercially friendly and less user friendly.