For an IGH the ultimate granny gear is Florian Schlumpf's Mountain Drive Crankset,
A planetary reduction gear, made for 3 and so speed hubs in his Swiss machine shop.

I got one for my Brompton, theres a special version for those,
with small wheels It has a big chainring ..

but when you engage the reduction gear it acts like it's way smaller my 54t ring in effect is a 21.6t.
the crankarms turn faster than the spider that the chain ring is attached to.

So below the low gear in my 3 speed Sturmey AW3,
is High gear in the hub in the reduction gear low range.. then 2 lower gears
in the hub.

Rohloff is doing similar , inside their hub, a 7 speed with dual range,
where they switch from low in high range #8, to High in Low range #7

the shift is a tap on the crank shift , a button where the dust cap would be,
and a flick of the 3 speed trigger shifter..