Totally agree. Drive belts are becoming a thing more and more, which I would deem to be a disruption. Far less maintainence is needed, no oil involved, no chain links, they last way longer than chains etc.
But these obviously only work on single speeds or enclosed-gear hubs. For derailleur-style gearing a change away from chains with the properties you described would actually really be a good thing, although I do not see it coming. With regards to power loss, chains get better and better, though.
They also only work with frames that have been specially designed to allow fitting a belt, as I understand it. Chains can be easily broken and joined in the shop (or even on the roadside), but not so with belts, so the frame must come apart to get the belt going through the rear triangle, which substantially complicates frame building and design.
I don't mean to suggest this tradeoff isn't worthwhile to people who want clean, low-maintenance bicycle drivetrains for working or commuting, but the extra cost of manufacturing makes it harder to persuade cost-conscious consumers.
This is true and a good point, but: It is hopefully only a matter of time until belts can also be joined and opened. Veers split belt [1] system already does this, hopefully this becomes more common, so the need for a belt specific bike-frame disappears.
These days you have Veer who offer a split belt that unlike the closed loop Gates belt can also be used with closed frames. But they still need to be manufactured to a specific length, unlike chains which are sold one size easily adjusted to all.
Absolutely! For commuter bikes, a belt drive is fantastic in it being very clean and low maintenance. And it's amazing how smooth the ride feels compared to a chain drive.
But as you said, it's either single speed or has a gear hub with less efficiency.
And for touring as well -- nothing like completely eliminating chain lube and cleaning equipment from your panniers. Plus, drive belts last something like 10-20k miles, so the price difference quickly pays off. Plus you don't have to worry about anything snagging on and breaking a derailleur, and belts work better in cold conditions, too.
I see them as the drivetrain equivalent of disc brakes -- sure, rim brakes are still around. But the tradeoffs are so worthwhile that you effectively can't buy a high-end bike with rim brakes any more (disclaimer: I know that certain touring bikes come with cantis by default, but they're rarer and rarer each year).
The only difference I see is that internal shifter hubs can cost 5-10% efficiency compared to derailleurs. In the commuting and touring communities, that's no big deal -- it's comparable to dynamo loss, which is considered a totally acceptable tradeoff for always-on lights in those communities.
But in the racing community, chains will probably stick around for a long time, at least until internal hubs lose that efficiency loss. There's just too much to lose in that 5-10% for racers, even if it's totally worth it for me.
But these obviously only work on single speeds or enclosed-gear hubs. For derailleur-style gearing a change away from chains with the properties you described would actually really be a good thing, although I do not see it coming. With regards to power loss, chains get better and better, though.