Rims with replaceable braking surface? Despite the movement to disc brakes in these days (even in the road cycling world), many still use rim brakes. Heck, even I still see rim brakes on our fellow MTB riders here at my place.

What I'm wondering is, why hasn't the industry produced rims with a replaceable braking surface? Especially with roadies drooling over deep-section carbon rims (which would be a waste if they get dissolved with every descent), I guess they could've made it for those who can't afford replacement rims.

Have they been already made? I've searched for them online but nothing's popped up so hit me up if there are any made.
Replaceable brake surfaces would add weight and complexity to the rim, plus make them more expensive. If they have been considered in history these factors would probably stop them taking off. 

Someone correct me if I’m wrong, but there would likely have been a frame builder and a wheel builder in most major towns historically. Wheels weren’t typically sold as factory built sets, rather you would choose a hub and rim and have your local artisan lace them up. Or do it yourself, bikes would need more regular maintenance and so more people had these skills. 

That is almost to say, braking surfaces were replaceable, if the braking surface wore down you would have replaced the rim. Nowadays that’s less common because wheels are cheaper and hubs aren’t considered so serviceable, we’re now likely to wear out both at the same time. 

Rims used to be made of steel, something else to factor in. 

Bringing it forwards, these carbon wheels (at risk of dissolving) have been the preserve of racing cyclists who care more about results than their wallet, and follow the example of the pro teams who are sponsored. 

Disc brakes came along and offer a replaceable braking surface along with other benefits, starting in the off-road world with harsh conditions. 

Meanwhile, the demographic of people who honestly can’t afford to replace their rims, either with the same one or a cheaper one, is small and small enough that the market hasn’t included them in the way you suggest. It’s cheaper to offer a thick, heavy, durable rim, than it is to develop a rim with replaceable parts; there isn’t an economic benefit. 

Just some rambling thoughts!