[gdal-dev] Which version number for the next GDAL release : 1.10 or 2.0 ?

[Even Rouault]

> 
> RFC 39 (the layer algebra) does break the C ABI, I believe.

No, it does not break anything. It *adds* new entry points, like all previous 
releases have done. Which is OK as far as backward compatibility is concerned.

> How about making the changes to the API but not implement them...?

That's an option that could be done for some changes perhaps, but to do it, 
you must have sufficiently thought to the implementation to come with a good 
API, and when you're at that point, you've already spent enough energy that 
it's better to do the implementation itself rather than coming back to it 
months later.
I'm not sure how users would deal with stub implementations of the API: that 
could be confusing.