The core is the central part of the network, the aggregation point for most of the data brought onto the network by the access layer. It also interfaces with other networks at peering points to create the internet.
Speed is the name of the game at the network core. Sending data where it needs to go as fast as possible doesn't come cheap at terabit scale. Management and configurability are also key.
The network core is typically focused on wired technologies, principally fibre technologies such as Dense Wavelength Division Multiplexing (DWDM) or high-capacity copper cable technologies for shorter ranges.
Although it may be harder to excite end users with core network upgrades, it's absolutely crucial that it keeps pace with the access layer. All that data isn't going anywhere if the core can't handle it.
What do we need from core for 2020?
Although not a full list, here are 3 important points.
In 2020, the network doesn't need to just deliver data. Applications and services are the real name of the game, so how can we enable them easier?