in order to have a wide range of gear ratios you will have a large differences in the size of the cogs, so you must have a
large difference the length of chain to be taken up, hence the need for a long cage rear derailleur..


the only exception Schlumpf Mountain Drive , because the low gear is a planetary reduction gear, not an actual 2nd chain ring..
But at 250% it's like you have a 50 and a 20 tooth crankset,
they are great when combined with another internal geared hub ..
the crankarms turn faster than the chainring.

or its alternative.. products from the same Swiss Machine shop.
overdrive for the planetary gears,[1.6x 0r 2.5x] and are fitted with the small physical chainrings for the lower gears. the chainring for higher gears, turns faster than the crankarms then.

the latter is recommended for Rohloff's hubs since they already are,10 out of 14 gears,
a multi stage reduction gear set.
there, it's a 7 speed IG hub, with a mountain drive low range shift
, inside the rear hub.