Not true. They upsell things like "early bird", since 2009 for example. And they charged for bicycle boxes as long ago as the early 90's. Charging for bags would use the same setup.

They do have some notable historical challenges though. Like foreign currency. They still cannot do that, despite flying to Costa Rica, Mexico, etc.

Bags aren’t managed in the same way as other ancillaries, because the prices are not linear. Indeed they allowed some special bags , but agents would have to manually check the aircraft was not over subscribed and organise handovers...

Regarding foreign currency, it’s a strategy choice on their behalf, they don’t want to own sales offices outside the USA

Trust me, I know a lot about this particular topic :)

They already "handle bags" in the sense that they are tracked to the PNR, issue tags, etc. They just don't charge for them. My examples show that they can charge for ancillaries. In fact, they charge for a 3rd bag or overweight today. It's not a technical limitation.