Not really. The bank stuff (where they are REALLY still running ancient mainframes) is not changing because its a bureaucracy and they're super risk averse. And every year the conclusion is the same - limp along for another year. Plus there are cases where the tech is so old that its essentially a black box at this stage.
On the authors scale - they're are few people that have the necessary odd combination of skills (accounting & programming). And those that do don't spend their time writing SME software...they work on enterprise scale stuff.
As for no incentive to fix it - trust me nobody likes paper invoices. Not even bookkeepers. Everyone's life would be easier if there was a widely adopted standardized system in place.
If you mean that the incentive is for companies to get legislation vague enough that it can be bent in different ways, I might agree, but even if they wanted to, it's really difficult to find a common way to account for both multinational biotech companies and individual stallholders in Chattanooga TN.
Its all good & well on a small business scale to DIY and integrate things hacker style but beyond that the actual accounting problems become big enough that you don't want the latest flashy gimmick adding potential unknowns. Its kinda like you don't run nightly builds on your production server.
As for the formats & integration - yeah not great. What you're looking for is essentially EDI, but there isn't a market for it on that scale. Its also still fairly fragmented so only works on an enterprise scale (i.e. BMW tell all its suppliers they are to use X standard).
Unfortunately in my experience (auditor) the more people try to hack together a solution the worse the end result. I've had to tell a CFO that all of their numbers from top to bottom are bad because they custom rolled a key component and the people that did so missed a subtle accounting nuance. Cost them a fortune to fix it. So yeah by all means go automate data transfer but please don't attempt to implement any actual accounting logic. Its like a airline pilot attempting surgery (or a surgeon flying an airliner). Neither even realises they're making a mistake until its too late.