One of the customers decided to migrate his solution to SharePoint. As far as I know, there would be an issue with the SharePoint threshold limitations.
There is like 20k items to migrate to primary list and will increase every year by 10k items.
That's a lot and there are some maintenance lists with a similar issue.
I was thinking about SharePoint Online Provider-hosted App and using external DB for storing the data. Have you struggled with similar issues? How would you deal with it?