Up to you whether or not you want to use it. I personally like this look much better than the thicker design as it more closely resembles the one from the original Ex Nihilo. I'll send you the JSON if you want but it's up to you.

Also, there seems to be a bug with filling/emptying buckets from Crucibles.

I was in creative. Why can't you take lava out of a Crucible while in creative?

you can, put the bucket won't get filled up, that is vanilla minecraft.
In creative a bucket will never change state, so when you try to pick up water with a empty bucket the bucket will stay empty.

Sorry, but I like the thicker model better, as it makes more sense to have thicker walls when you store molten stone in something.

And the bug with the buckets, could you please elaborate? Taking fluids out works in for me, and putting lava back in is not supported (not not make problems with the current smelting process when there is a different block smelting). Are you sure you were not in creative when taking the fluid out with a bucket?

Yes however the thin crucibles require changes to client.renderers.RenderCrucible, and you can't do that in a resource pack.

And I'll have to disagree with you there about it "making more sense" that the walls be thicker, as by that logic you should make the stone barrels thicker as well. I'm just stating what I think looks better though.

Oh, that's strange.

I also had another thought:
Would you consider allowing the look of the Crucible to be configurable so that a modpack could have either the fat crucibles or the thin crucibles?

And what about the original Stone Slab barrel?

if you still want this to be in I you could send me the jsons and I'll try to see whether it works

Alright, here they are. This should be everything needed.

Lines 45 - 48 in client.renderers.RenderCrucible must be changed to this:
https://pastebin.com/V1vFUnqD

Here are the textures:

Here are the Jsons:
jsons.zip

Welp, better late then never, but I finally got around to implementing this. ^^