Differences in Next Gen Network data centres
I learnt something today I didn’t know about Linode - the new data-centres (Mumbai, Toronto and Sydney) are built with so-called “Next Gen Network”. 
NGN doesn’t seem to (currently) support some things (such as IP Sharing.) 
I’m intrigued with what the difference is with a DC using NGN compared to a non-NGN DC, such as London.
Will the non-NGN DCs be upgraded at any point in the future?
Will the new beta features, such as Cloud Firewalls and VPC/VLAN require a DC using NGN?
This is a great question. The short answer is that we were experiencing some growing pains with our existing networking. As Linode expanded, we realized that the existing scaffolding wouldn't allow us much flexibility in regards to automation and scaling. NGN makes use of Cumulus Linux and Mellanox products and allows us to use open-source tools to orchestrate, automate, and monitor our infrastructure. There are also some physical hardware differences between non-NGN and NGN data centers. NGN makes use of newer Mellanox hardware, as compared to older Cisco products. We also switched from 10g connections to 25g at the host level, which are much faster. Our Director of Infrastructure Operations and Network Operations Manager discuss NGN in greater detail in this webinar. Their section starts at minute 26.
We continually upgrade the hardware in our data centers, so moving forward you can expect to see more of our data centers offering the Next-Gen Network. As for new/beta products that are currently on our roadmap, Cloud Firewalls will not require NGN, but VLAN will require NGN.