I'm not sure from the doc what sorts of query use-cases you're trying to support. Are you saying that the flakiness dashboard and sheriff-o-matic would talk to this datastore?
I think the flakiness dashboard will likely be the most complicated consumer of this in terms of the demands it places on the datastore (it's both a lot of data and needs to be near real time). We should flush out an end to end design for the flakiness dashboard to make sure it would work. szager and I have been talking the past few weeks about reworking test-results.appspot to work better for the flakiness dashboard use-cases. Just coming up with a dedicated solution for flakiness dashboard that works well has proven difficult. We have a plan in mind now, but it's not general.
Of course, if we could do something general with your datastore that meets the requirements, that'd be much better. It might be that the conclusion we come to is that test-results/flakiness dashboard is a special case and that this datastore should be for all our other storage needs.