Basically this is a suggestion to allow the user to add custom block types to be used for the beacon amplification mechanic, whether those are modded or vanilla blocks (but realistically for modded blocks designed to be more valuable than netherite).

Prime example in my case would be the Advanced Netherite mod, which has new blocks of Netherite-Iron all the way to Netherite-Diamond. I would personally config this so Netherite-Emerald is +4 and Netherite-Diamond is +5, for example.

You can already do it. Take a look at the wiki to see how to add the blocks.

Ah I didn't catch that, thank you.

Do you happen to have an example datapack with the folder and file structure for this? I'm not exactly sure how I'm supposed to setup the designated folders.

Use this path for the folder data/better_beacons/base_blocks_amplifier and then create the Json file. There is an example of how the Json file should look like in the wiki. Or look direct into the source code, Example