The 12C27M was developed as a kitchen steel. Seeing how Buck just jumped back into the Kitchen knife business its a good guess we will see that steel there.
The 13C26 has very fine grain structure and was developed as a razor blade steel and apparently Sandvik supplies most of the US razor blade guys. It takes a very sharp edge and is supposedly good at edge retention and easy to keep razor sharp with regular touching up. Kershaw is introducing a replacement steel this month it developed with Sandvik (14C28n, I believe) so I wonder if Buck picked up the 13C26 production previously allocated to Kershaw???
Anyway, I hope that this is not the end of 154cm at Buck??
It will be interesting to learn about the new models. g