Thanks for the feature request, good input. Note that these community forums are not the best or official way to raise an FR, but definitely send your ideas and use cases through your Meraki sales team, or through your Cisco/Meraki Partner to bounce to the corresponding Meraki sales team. They can confirm if your FR is already in our system, and if it is, add you into it, and if it's not, perhaps create the FR and update the MV team with your input.
I have no roadmap info to share, but motion based alerting is a common request. The issue is that we've all seen motion based alerting before, and in many cases there can be so many alerts that it only trains you to ignore them. Time-based motion alerting might only help so much. So while I'm sure such a feature can and should be developed, I'm sure we're going to want to make it "smart" so it would only send you alerts when there's some meaningful or significant type of motion to report, and that gets pretty complex pretty fast. Anyway, stay tuned, and keep reporting your wishes and use cases so the team can categorize and prioritize feature development.