Originally found by Wowhead, a small build was pushed to a separate Season of Mastery build over the weekend which included many new and reworked spell IDs that will likely be coming to the next beta update.
There are four new spells that hint at the possibility of hardcore support, although there is no way to confirm this until official word from Blizzard.
The Soul of Iron, Survivor of the Flames, Never Known Defeat, and Thousand Blades are the new spells that all have reference to a Hardcore or Iron Man mode.
In the same build, Warrior's Diamond Flask was nerfed to not stack with +healing gear, bonus experience tokens were found, and the first potential fix for mage boosting was found.
WoW Classic: Season Of Mastery Might Be Getting Hardcore Iron Man Support By Blizzard
Hardcore or Iron Man game modes are typically unique characters players create and have to obey a specific set of rules, such as no grouping with other players, no using items or gear you did not find or craft, and you only have one life.
Considering the Season of Mastery is being created as a way for players to replay the original version of the game, it fits well with the Hardcore mindset, as many players who choose to create these characters are doing so to replay the game in a new and fresh way.
While it is too soon to guess what Blizzard's plans are for Hardcore Iron Man support, it would be nice to see a separate realm created for these characters much like the different PvP, PvE, and RP realms today.
Be sure to check out the new Beta patch that is expected to go live sometime after the weekly maintenance this week to see if this new build is included in the update.