Need to Automate Time Reports

I want to implement automated time reports sent to individual users, especially those whose time entry is below a certain threshold for the week. Now, I see there is a Time Tracking REST API, but it has mostly methods for changing system-wide time tracking settings and ones for managing work items for a particular user. The only GET method for work items is for getting those of a particular issue. I need one that allows me to query work items generally - for a particular user in a particular time frame, for instance. Even a broader one that returns all work items for a particular period of time would be useful. So are there any undocumented methods of the Time Tracking REST API that would allow that kind of access to work items?

I might also be able to work with a Time Report if I could get a report from the REST API in JSON format. I noticed the time reports use REST URLs (e.g. /rest/reports/time/Weekly%20Time%20Report%20-%20Work%20Author) and I've found that I can add /dataView to the end of this URL to get the report table HTML only. Is there a way to get this report to just return JSON or something comparable?

Also, will we be able to access work items in custom workflows at some point?

Thanks.