Markus - are you suggesting retroactively referring to, say, version 1.5.1 as version 5.1 - with a corresponding change to all the documentation, etc.? Or just jumping straight from version 1.9 to version 10.0? I'm assuming the latter, but in either case that seems like a bad idea, that will in fact cause confusion, without any obvious benefit.
Yes, Java did it, but, as Wikipedia notes , that was strictly for marketing purposes, presumably because "Java 6" looks a lot nicer on a book cover than "Java 1.6". Behind the scenes, Java developers still refer to it as 1.6, etc. When the first "SMW Unleashed" book comes out, then maybe it makes sense to start talking about making the number look nicer. :)
I think it's overly dramatic to say that SMW versioning will never move past 1.x. There are a few previous versions that could have merited a jump to 2.0, in my opinion - the most recent two, 1.8 and 1.9, being obvious candidates. Perhaps it was a mistake to not make the major number jump with either of them. (And by the way, maybe it's not too late to rename 1.9 to 2.0? It's only been out for two weeks now...) But trying to pretend that those *were* major version number changes seems like it would cause more problems than it's worth.
Jeroen - the numbering decisions of the developers of core MediaWiki seem irrelevant to this discussion, I would think.