Wow Okay.
This isn't baseless speculation.
We know that Idoneth will get Endless spells. We don't know when, but considering the breakneck speed of new battltomes this year, and new versions of AOS 1.0 battletombes, it seems likely in the next year and a half.
And we know that that the rumor engine picture included details that match up 100% with current and unique idoneth sculpts, (the vase and chest). These aren't generic details, they match current Idoneth bits perfectly.
It is entirely possible that the rumor engine pic belongs to a non-idoneth model, (like another races treasure hoard, which includes stolen idoneth stuff) , but linking it to any other faction is pure speculation, which is also fine. Gold coins are generic, but the chest and vases are uniquely Idoneth, and so they are the only known faction linked to that rumor engine preview by more than speculation.
But considering that we know Aos 1.0 battletomes are getting updates and endless spells, and considering that we have now seen rumor images showing as yet unreleased miniatures bearing distinctive idoneth design, it seems convincing that the two are related.
You can say the faction doesn't need anything new, and decry it as mere speculation, but then everything in this thread is speculation, and this at least is well grounded speculation, based on observation of current trends, and miniature previews.