> In particular, it describes how the system must allow some non hereditary class movement. If the class system is too rigid, pressure builds up as talented individual press against the ceiling.

Thats basiclly lenins great innovation. If you look at the leaders of the USSR, you will see people from all around the empire, while in the older system you would have the older familly based fudalism.

The soviet dream, get into the low levels of the party, work yourself up. That was not possible befor.