No and stop asking for it. Even if they would add that to Siege of Orgrimmar somehow (which it never was in 5.4, it was just a raid difficulty), they would still have to implement that on 4 different raids which were never designed with that in mind. Good luck balancing flexible Animus, it wasn’t even balanced with 10m/25m.
It’s like asking for 10m/25m in TBC because Wrath has it. Or heroic raiding.
What mechanics? They have never touched any raid systems in Classic except buffing some item levels in Ulduar during Wrath Classic.