That's a single scenario (focusing on the 'obsolete' part), and android users buying iPhones has the same effect (additional cables for no functional difference)
There's an infinite number of cases where getting rid of the lightning spec would reduce the number of cables.
A household with an iPhone and an android user would also buy an extra set of cables that could be avoided. Even having an iPad in the mix generates cable duplication: the iPad Pro is on the different connector, android users buying an iPad is also more common than one would think.
Broadening to charging stations in waiting rooms, shopping malls, cafes etc., including other portable devices like headphones, portable batteries, cameras, etc. and the iPhone having its own non standard and connector is more and more a waste.
If there aren't enough iPhone users to worry about, then why force us to replace all of our cables, chargers, docks, etc?
You can't have it both ways!
One year ago, there were 1.4 billion[0] of us, each with one or more (many more, in my case) cables, docks, cradles, etc. That's a lot of waste to churn up for "not enough iPhone users."
An iPhone user buying an android phone will need a new set of cables, his old lightning ones have no purpose anymore.