From the L5R Discord:
The Itsy Bitty Spider - 01/04/2019
The AEG story was about to do Onyx Edition, which was when Spider succeed in conquering the empire, going back to their horde roots and forcing the surviving clans to flee to the colonies to have a re conquest arc set a couple generations later, with Rokugan invading the Spider this time. It's set up was far more interesting then it sounds on the surface, since clans were being given choices on HOW they wanted to end before the time jump.
Because it was also the 20th anniversary of the game, they wanted to bring back Naga after the time jump, because THAT was a popular faction that people totally wanted lol, but they needed to make room.
Since Mantis A) shared ALOT of mechanics with the Naga, B) was the least played clan with the smallest fanbase according to the Imperial Herald and C) didn't mesh with the Onyx setting as a whole, the plan was that Mantis, the entire fucking clan, die buying time for the emperor and survivors to escape the Spider by sea. There was an entire set that was based on the Mantis going down like champs fighting sea monsters with fucking metal as shit art.
They announced this decision, then EVERYONE lost their shit about the Mantis, except the mantis haters of course, but the pressure led to AEG promising to let a few mantis survive and bring them back later, but in the mean time giving the Mantis all these cool options for HOW they come back... but Mantis chose to come back the exact same. So instead of Removing the mantis and replacing them with the Naga, they were now promising to have to juggle BOTH factions together. It was going to be hilarious.
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The following text is from r/l5r:
kempy_nezumi, 08/18/2021
About Onyx/Mantis
As Onyx base set and first expansion of this edition were nearly developed and finalized, we know that there's no Mantis Strongholds there. All Personalities from exMantis are Unaligned. But... There were also special Senseis that allow specific Family to join some Clan and be Clan Alignment to it (Moshi, Tsuruchi etc.). That how "no Mantis" was meant to work.
PS. And Naga stuff was much enjoyable to play than Mantis for last 5+ years of CCG. No more economic warfare stuff, no more Naval, but lot of recurrsion/copying and also some Pearl magic. Similiar themes were Ranged Attacks only, and maybe Commanders/Followers