SharePoint Search to extract SharePoint list Data into SQL

Problem:  I have multiple lists that I need to get data changes updated into SQL on multiple site collections.  Think 1000 site collections with 5 lists in each so 5K lists are being updated (my actual requirement is much larger).

Initial Hypothesis: In SP 2010 or SP 2013 I would use a Full Trust Event Receiver and register each list using a feature but now we are in the new world of no full trust code.  The 1st thought is RER (Remote Event Receivers), I need to register 5,000 of these and they are notoriously unreliable for delivery.  Search has to pick up all changes to list items for indexing and I can break into the crawl pipeline during Content Enrichment.

Proposed Solution:

Points to Consider:

1. I need to create a Content Enrichment Web Service (CEWS) that I shall call from the crawl component.  I can only register a single web service on a crawl SSA so consider using the toolkit/Microsoft CEWS Framework on the Web Service endpoint this allows multiple Web Servies to be strung together.  Good idea to implement a toolkit so multiple pieces of logic can be applied.  So if BA Insights registered, then can't add another CEWS Web service. CEWS toolkit provides a pipeline of stages to add custom logic later.  So write our own stages and hook into the CEWS framework.
2. CEWS does not process item deletes so a possibility is using the crawl log to identify deletes
3. There is no CEWS on SharePoint Online/O365.

Note: Properties returned from CEWS has minimal data input (common custom fields such as Title) and need to augment with registered MP's to get the data in the CEWS web Service.  Do not get a dump of properties/need to register and ask for the properties.

27/04/2017 Note: An idea I had to deal with "Deletes", I could put the item into a status of "About to Delete" and the crawl would pick up the status and the CEWS could delete from he SQL database and then the Web Service could delete the list item from the SharePoint list.  It doesn't work, the CEWS pipeline does not pickup and item updated and then deleted.  So the crawl is smart but I can't enhance using this approach so more work to fix the delete ...