Properly normalized data isn't just faster, it's also easier to work with for the end user. There are much less exceptions, edge cases and snafus to work around and test for. If you're talking about the transition period between formats, well yeah, you're gonna see things breaking. But these were already broken, just not in apparent ways. In the end, everybody wins.

I guess I don't follow your analysis.

People doing mapping tasks will use an editor and not really see the change.

People consuming the data will also mostly use tools, tools that likely run much faster.

I've written some code to chop up overlapping gis areas into ways and relations (to match the current data model of references to shared nodes). The input to that code is pretty close to the proposed data model, so not going to be more difficult to do that processing (as an example of a task that doesn't just use 3rd party tools).

It is plausible that data format can be made better for everyone at cost of very significant redesign cost of software interacting with it.

> Why not just create accelerators based on an intermediat format?

making things easier for mappers by introducing new data format requires changing format used by mappers

End users don't work with data format directly. They use tools and these tools could be better, if data format was improved.