Considering how Minecraft physics are almost laughable even in the Newtonian realm (for example, you can compress/store 27x64 cubic meters of cobblestone into a 1m cube/chest) nitpicking on the implementation of quantum concepts is a waste of time. This isn't intended as a rigorous treatment, it's an introduction to the concepts and how they would impact if they were visible at the macro scale. Personally, I think the implementation of superposition is reasonable - the block is in an undetermined state when it's not being observed and has it's state frozen by observation. Switching states after being observed isn't quite kosher without some other interaction, but I'll live with that for the sake of gaemeplay. Maybe a redstone signal could be required to destabilize the state of the block after being observed. The Observer dependency is a bit more problematic with its directional dependencies, but I can't think of a good way to implement that in a game. In theory we could use redstone as an activator again and selecting the state of the block probabilistically based on available observers and their distance from the block, but that's a fairly complex algorithm to run in realtime, updating every 1/20th of a second (the Minecraft tick/sampling rate) in Java.
The entanglement doesn't seem to properly describe the quantum phenomenon at all. Action at a distance != teleportation. The trouble is a realistic implementation would probably be exploitable in game terms. For example if you have 2 of those entanglement altars (or whatever they are called) and you place a block in one, I would expect to see the same block appear in the other one. Now how do you prevent people from using this to clone valuable blocks like diamond in game? In multiplayer, with 1 player at each "altar" you would have a very tight time sync requirement if both players tried to mine a block in their respective altars simultaneously.
An alternative mod spotlight.
https://www.youtube.com/watch?v=1HI-keffxmA