Anyone building software that catalogs imagery or other geospatial assets is welcome to collaborate. Our goal is to be a collaboration of developers, not architecture astronauts. A number of developers met in person and sprinted on specs and made a number of key decisions.
The best way to contribute is to try to implement the specification and give feedback on what worked well and what could be improved. Currently there are a few major things to still work out, so if you are interested in implementing you should jump on our gitter channel and check in on how ready the spec is and how you can support it. For the next bit of time you'll probably be encouraged to just do what feels best in some areas, so we can capture best practices and standardize.
Any proposed changes to the specification should be done as pull requests. Please make these requests against the dev branch (this will require you to switch from the default of 'master', which we keep so it displays first). Ideally a proposed change would also update all of the examples, but for now that is not required - the team can validate and update all examples before a release. But it is recommended to update at least a couple examples to reflect the change.
All pull requests require a review of two team members.