Proposed solutions I have seen, or that I suggest (with pros and cons) pt4:
Eureka Mobs giving Centurio Seals + counting for achievement (after the consolidation of the Allied Seals + Centurio Seals currency)
This would certainly help, as it would keep Eureka relevant for those who do not wish to wait for A rank/S rank hunts, or are not involved in the Hunting community at large. Additionally, if it counted towards the A or S rank kills, players whose sole mission is to farm Hunts for the Centurio mount / achievement would instead dedicate themselves to farming Eureka, which would further help in making -- and keeping -- the Eureka content relevant outside of the Relic Armor.
Thoughts and feedback are more than welcome, as I love to hear what other hunters think about these issues -- or in some cases, perceived issues -- and proposed solutions. ...I'm very passionate about hunting content.