I’m a big gearbox fan, and IGH too (I have a few), they have loads of benefits, drivetrain longevity, weight distribution, unsprung weight advantage (not IGH!), dish less rear wheels, weather sealing to name a few, the problem is the drawbacks, not individually…if they were just a few lbs heavier it would be ok, if they were just a bit more expensive it would be ok, if they were just a little draggy it would be ok, it’s the fact that they are heavier AND draggier AND more expensive that holds them back.
Solve any one issue and I reckon you’d crack it, a budget but reliable option would be ace, a zero weight penalty likewise, e-bikes may help nullify the draggy aspect and reduce the weight disadvantage though so interesting possibilities ahead methinks…