I don't think RK3399 support LTE, but not sure. Perhaps they had to use a MTK chipset for that, but they are rockchip partners, so I suppose that's why they continue using RK.
It's primarily aimed at setup boxes so it's very unlikely. Actually I doubt RockChip has the needed IP portfolio to create a on die LTE unit.
"In addition to application in tablets, VR, TV-BOX, laptops, in-vehicle navigations, and communications, the RK3399, with its enriched scalability, can be applied to all types of terminals covering industrial and consumer applications, including smart appliances, advertising devices/the all-in-one machines, POS systems, vehicle control terminals, thin-clients, VOIP video conferencing, security/monitoring/policing, IoT, as well as other fields. As the new flagship product of 2016, Rockchip RK3399's strong compatibility and scalability is its strongest core competency.
Rockchip Flagship Solution RK3399 Release! --- High Performance, High Scalability, and Versatility
IoT and tablets give a slight hope but they don't list it so almost definitely nope.