They go way back. All the way since the start. A lot of people believe they are connected with Raxxla, some people believe they are some key. But one day, completely removed from the game. No trace of them. Had a friend who asked support why his Sap-8 Container disappeared, they said a long the lines of "They have been removed from the game" It was rumoured they were around still but nobody ever found any. In the end people gave up. Then suddenly a week after the new patch comes, people are finding them again? They have suddenly come back. But, the question is, WHY?
Oh, that is interesting!
It could've been that they were created ages ago with the Guardians in mind for future prep, but ended up in the game by accident (it has happened before with numerous bugs)...
This re-emergence is very interesting...
Where can we find them? Could be worth doing the following with the SAP 8 Containers:
1) Take them and try them in Thargoid Bases
2) Take them and try them in Guardian Structures (Data Core)
3) Gift them to Thargoids and see their reaction
Oh, and from the wiki:
http://elite-dangerous.wikia.com/wiki/SAP_8_Core_Container
"This container holds a crystalline shard of unknown origin. Scans indicate that the foot long shard is suspended inside a modified, self-sustaining, fusion-core containment field. Any breach of the field will result in the containers destruction."
Sounds suspiciously like a Guardian Relic if you ask me

However, it could be a different type of relic...