This was a very interesting section for me, especially since I am unfamiliar with a lot of the DC systems being almost strictly an enphase installer.
Enphase microinverters certainly make solar simple. It is amazing how fast the technology and Code changes. What I was teaching 5 years ago is much different than what I am teaching now. We did have Enphase since 2008, but now we are having Rapid Shutdown requirements, grounded inverters are now rare, multiple MPPT inverters are normal, power optimizers are very common and 3-phase 480Vac/1000Vdc systems with string inverters are the commercial PV system of choice.
What will the industry look like in 4 years when everyone is using the 2017 NEC?
Perhaps all rooftop PV in the US will have module level electronics, perhaps all ground mount PV will be 1500Vdc and our racking systems could be all rail-less and perhaps some composite, non-metal racks moving into the market.