I had run into this when I first started playing. This was right after the new rail system was released A lot of blueprints had the old dockers on them. "How to" videos on youtube had instructions on how to build turrets and dock your ship using the OLD dockers. But how would one build the ship if they could not make the docker blocks? And even if someone did somehow get the blocks.. the docking mechanism no longer worked, and the blocks did NOT inform the player that they were depreciated blocks.
The solution I came up with was to hunt pirates, since pirates would drop ALL kinds of blocks, and I could get a few dockers that way. Haha. Though.. Then the problem was the blocks simply didn't work and I had no idea why. I spent HOURS trying to make this work. I don't think that is an intended feature of gameplay. On LvD we had to disable loot drops though since people could get thousands of gold bars hunting pirates.. Not good.
So I think it's really up to servers to decide how to deal with these old blocks right now. Some servers might re-enable recipes for the old blocks so they could still be used decoratively. But I would agree with you on your solutions. By default, I think all OLD blocks should still be craftable, even if their functionality is removed. Their names also should be then changed to include the word "decorative" or "depreciated" though and their ability to connect to modules and things should also be disabled, so it's a bit more obvious to new players that these blocks are no longer to be used as functional blocks. Perhaps even include in the description of the block WHAT feature replaced the blocks, to point new players in the right direction on what they need to learn.