The original Kitz page on 21CN shows 10G links from Metro nodes to the Core (and within the meshed Core too), but I guess things have definitely moved on on this front.
They did a massive upgrade and overhaul of the 21CN core last year.
They heavily invested many hundreds of Alcatel 7750s - not just for the MSE's either. These are capable of taking 400Gbps of traffic on to the Core.
Ah yes. The MSE BRAS is a project I knew they were doing, but I hadn't really thought about. Or at least it hadn't registered that it implied such a big upgrade of the core.
When you look at Neil's slide on their current network architecture, I guess those are the "Service Aware Edge" boxes, located (by number of sites) at all the metro nodes.
Slide at this point in video:
https://youtu.be/5ZU5tvBUwZM?t=101