Its so low you dont even see SR based AM3+ parts.
AMD could easily build a 4 module SR chip, but why? It would be 28nm bulk and perform worse than the 32nm chip it replaced(just like kaveri did).
Even if they had a node capable of producing a faster chip, it would be shackled to AM3+.
AMD's big die platform hit a wall, with no way forward. Progress would require a fresh start: New arch, new socket, new process technology.