Making my prediction now:
My thought process is the prime upgrade system is treated similar to relics, Eikon being the '1 byne bill' eventually needing a 100k byne bill, but obvious not at that scale.
We know having stage 1 in inventory unlocks stage 2 rocks (Eikondrite) to drop in the upstairs, logically the next step will be the downstairs.
Having stage 2 unlocks stage 3 rocks to drop from the basement. Need more than 1 to get to stage 3, unlike Eikondrite. Maybe 5-10?
Having stage 3 allows for a trade? w/ Ruspix, need multiple Eikondrite and/or t3 stone to purchase t4 stone via a chunk of Galli, maybe even 100k. Ratios unknown, but more than previous.
- This is mainly copium... most of us have well over 100 Eikondrite and would like it not to have gone to waste.
Final stage requires further gathering of rocks and trading via Galli to purchase a shiniest rock, and in addition you'll need 1 of the other datamined item, 'Voracious Psyche', per Prime Weapon which is a 100% drop from Aminon? This would be the "shocking" aspect of the final stage since very few people actively pursue fighting him.
Fully expect the final Valhalla arena to be strictly for the final fight and be solely linked to acquisition of rings. Similar to how the Hades arena is only used for Hades and nothing more.