The Monotonic Versioning Manifesto looks interesting. Here’s the summary. Version is composed of only two numbers: X.Y. No leading zero is allowed for both numbers (so you must start at 1.1, not 0.1 nor 1.0). X indicates compatibility and must be increased whenever you introduce a backward-incompatible change. Y is the release number and must always increase, even though X is increased. In other words, Y is never reset. In this aspect, Y is akin to build number often used in compiled projects.
If you maintain two versions of your software, e.g. 7.5304 and 8.5822 and want to backport some feature/changes from version 8 to 7, you would release 7.5823.
Oh, and one more thing: since the popular semantic versioning scheme uses X.Y.Z, to aid interoperability X.Y.0 is allowed as an alternate display format and is identical to X.Y. Any other number for Z is not allowed.
Sure, the numbering scheme won’t be sufficient for larger/complex software, but for many Perl modules it could be a fit.
The important thing is to decide the number of digits you will need for the release number. 1.1, 1.10, 1.100, and so on are all the same in Perl (this is according to version->parse(V1) == version->parse(V2)), so you cannot just start with 1.1 and expect to go more than 9 releases without increasing X.
A sane choice is either 3 or 6 digits*). If 3 digits is enough for you, then go for it. A total of 900 releases, ever, sounds limiting at first but I don’t think there is a CPAN distribution that has close to 900 releases, are there? Otherwise, go for 6.
*) Because the way version number works in Perl, you should not choose e.g. 2 or 4. Because version->parse(“1.10”) < version->parse(“1.9”) and version->parse(“1.10010”) < version->parse(“1.1009”).