We have a "meta CI" system called bors/homu that integrates with other CI, currently Travis and AppVeyor. bors works with any service that can post a result to a GitHub PR.
So the plan for supporting further architectures is to create a small custom runner that builds, tests and posts to the PR. That code does not exist yet, but if it appeared there are likely several upcoming architectures that could make use of it.
With that tool, we could allow contributors to set up their own integration bots and hook into our CI.