Why do you and Ramsey see MTM as a parallel rather than a competing/successor technology?
The one looks like it is capable of authenticating access to a single network (the mobile network), and the latter can grant access to multiple networks (including a person's corporate VPN and all of the mobile networks).
In the US, the SIM card seems to be used as a tether by mobile service providers. MTM seems to release the tether. I would imagine this might explain the slow progress in introducing it.