Is there a reason for this? If you have such a set up, do you like it, or does it limit the bike's utility in other contexts?
in St Louis Missouri I doubt you will need the wider range differences that 2 chainrings offer..
lots of simple cruiser bikes put a rear derailleur on for more gears,
there are multispeed internal hub gears, too.. they cost more to include.
I dropped the big bucks for a 14 speed IGH .. Columbia River valley is different than the Mississippi