5G has plenty of benefits for the mobile operators themselves (like increasing the amount of bandwidth they can offer from the same amount of spectrum) but the benefits to consumers aren't so obvious. Don't expect that to change much in 2020; 5G will still be a technology largely in search of a killer application.
Slowing refresh cycles mean that it will take a while for 5G phones to become common, and in any case 5G networks are only being rolled out gradually. Rows over the politics of 5G could still slow those roll-outs down further, as could a whole new set of 5G security threats.
It could be late in 2020 by the time a 5G iPhone arrives: only at that point will 5G really become a mainstream technology for consumers, at which point low-latency gaming and AR and VR apps might start to take off.
However, it could be that the defining usage of 5G in 2020 is by the enterprise. That might not mean developments as exciting as the 5G ambulance, but Internet of Things applications, which make industrial processes more efficient, and edge computing will be key. Not as glamorous at AR gaming, but maybe more useful.