Would it be possible to add mob spawners & Amethyst Geodes to the shape renderers?
Also if possible to show the mobs spawners spawn distance (16 blocks)?

much appreciated, fantastic mod <3

What would a geode renderer even do? The shape renderer is mostly for used-created/added shapes. You can already get an approximate spawner spawn range by using the generic sphere shape with a radius somewhere around 16.

And I'm not sure if I want to add an overlay for finding dungeons/spawners, as that to me feels like x-ray type of feature.

The structure renderers don't render through blocks by default, the ship wreck and treasure boxes are kind of a weird case because those are in the air instead of where the actual structure generates below, so they are easy to see because of that... So if the dungeon renderer would also not render through blocks, would it then even be useful for anything? Or did you mean just a spawner activation range renderer for the spawner?

AFAIK neither dungeons or geodes are actually structures, so there is no good way to find all geodes or to render anything about it, other than checking all blocks in the world and then creating a shape around it. Which I don't really want to do nor do I think it would be that useful, unless it would render though blocks. Spawner at least can be located a bit easier since they are block entities.

I have also considered adding options to allow all renderers to render though blocks. And with the upcoming malilib versions the server can disable any features it wants, so maybe it wouldn't be a huge problem even if some of these would be capable of rendering though blocks. I might make those render-though options opt-in from the server though.

Shape renderer possibly not the correct term, Structure renderer?
Amethyst Geode, would be same thing as Nether Fossil I guess?

Dungeon spawner would really be no different to any other feature that's not immediately visible, shipwreck, buried treasure, mineshaft for example.
Intention was not for xray, but replicating features that Bounding Box reloaded has, since I prefer your mod :)
For example, when building a blaze farm, handy to see the spawn range as its not a sphere so that all spawning attempts are encased.

the fact it doesn't show through blocks would negate the x-ray concern.
and you are right they are not structure's as such, but

I'm sure you know this..
Mobs spawn in a 9x3x9 box around the spawner block,
there is another bounding box 16x9x16 where the mobs are no long within the spawner mop cap range (allowing more to spawn)
Then obviously there is the 16 block radius around the spawner for where the player has to stand for them to actually spawn.

just installed BBOR to take this screengrab as an explanation.

this is the 9x3x9 spawning box, so you know to clear out that area to maximise the spawner.
there is also a line showing from me showing the activation range, (goes red when not in range)
However, this mod does render through blocks, making it quite cheaty (another reason not to use it)

By render through blocks I meant with depth test disabled, which would make the shapes visible through all blocks and obstructions. In those screenshots depth test is enabled, ie. what I meant by not rendering through blocks. I didn't mean that it would only render when you can actually see the spawner block.

But yeah if these activation ranges are what you actually wanted, instead of an easy way to locate the dungeon by rendering the box through all terrain, then my earlier concerns don't apply. I can definitely add these type of renderers for spawners.