Since there are already official WordPress coding standards https://github.com/WordPress/WordPress-Coding-Standards, I think there shouldn't be another place with sniffs?
The custom "PluginCheck" sniffs should be migrated to the existing coding standards, as well as the ruleset.
If for whatever reason that isn't possible, the custom plugin checks should at least be published as a standalone rulesets (one that includes all, and only sniffs created by this plugin), so it can be used standalone too.