I know that https://cloud.weave.works somehow includes or uses hosted prometheus. Haven't tried it though.

The 2.0 release of prometheus will help with stale data but not support bulk import yet. For that you can track https://github.com/prometheus/prometheus/issues/535

But to be clear: My service isn't about running Prometheus off-premises. It only provides the metrics which you can gather with your own Prometheus servers.