In vanilla, there are two different rendering types used for rendering translucent blocks in the world according to the wiki's "shaders" page: there's "rendertype_translucent" used by water, ice, slime blocks, honey blocks, tinted glass, stained glass and its panes, and nether portals, and there's "rendertype_tripwire" which is used exclusively by tripwire.

I'm not sure if making tripwire an option that certain blocks can use via block.properties would be possible at all since I don't know if there exists a distinction between a "rendertype" and a "block layer".

The behaviour of rendertype_tripwire is quite strange - I've reported https://bugs.mojang.com/browse/MC-261837 to keep track of it. It appears that from some angles, it occludes all other tripwire blocks behind it, like how translucent blocks rendered before release 1.7, but from other angles, no culling happens at all.

Why should tripwire be an available layer?

In vanilla, tripwire_hook isn't set to render like tripwire does, and instead uses the normal cutout rendering (I believe). This causes the section of tripwire that's connected to a tripwire hook to look noticeably duller and darker than the main tripwire itself, which is an inconsistency that I don't like very much. Having the ability to change this to use the tripwire's rendering would resolve this issue.