In the extensions I've written, I've usually used the x.x.x naming convention, similar to the MediaWiki core's. But in light of the comments made in this conversation, I considered using integers. E.g. advance from version 9 to version 10 rather than from 1.1.9 to 1.1.10, and thus avoid confusion about which version is after another. However, that eliminates the ability to use the version number to denote major releases.
I haven't seen very many decimal systems in which, say, version 3.31 was a minor improvement over 3.3, since the DOS era. The new standard seems to be the type of system MediaWiki uses. And for good reason, because it defeats the point if, just because there are only 10 possible digits in the base 10 number system, you have to go from 1.1.9 to 1.2.0 even though it's not a major release. I see pitfalls no matter what we do, but the current version system is probably the best option available. We may never reach version 2.0.0, but we leave the door open for it.
Speaking of extension versioning conventions, I wonder if my using the x.x.x convention will generate confusion as to whether the extension's version or the compatible MediaWiki version is being referred to? - Tisane