There is a pretty big difference between archival and deletion.
They could be implemented in a similar fashion, but semantically they mean very different things, and combining them into one feature could have unexpected consequences, both for UX and for general integrity.
For example, systems that have a trash feature inevitably also have an “empty trash” feature to easily and quickly clear them permanently. I see no reason why this wouldn’t be added here as well. But if I “delete” an item in order to archive it, I (or someone else with adequate permissions) could accidentally empty the trash without realizing that it was holding at least some items just to keep them from being searched.
Also, if I archive an item and then later delete it from the archive, I’d expect the item to be moved to the trash just like every other non-deleted item. Maybe I deleted the item from the archive by mistake…
So there are quite a few use cases that indicate that these should be separate features. The only two things I can think of that they share is that items in an archive or in a trash should be hidden from search (or even just the regular list of items) unless they’re explicitly being looked up, and that they should continue to respect their original permissions from before they were archived or trashed.
Both features make a lot of sense, though I personally came here looking for an archival feature. Whatever the case, it’s really important in my opinion that they be kept separate.