Hi Steve
Satisfying the requirement of interim load updates makes it way more complicated than it needs to be. If you have source file loading of 500,000 records if you had an update every (N=)10,000 records that's 50 updates, and more if the value of N is bigger.
The problem is no matter what you set the number N for number of records, unless set at N=1, for an update you can technically have a load file with less records than that, which mean you'll never see that update.
The reassurance of your client should be gained from validating the data before load and validating records loaded successfully afterwards. That gives them confidence of the DQ and information about the load file like number of records etc.
Thanks for posting an example of a seemingly simple non-functional requirement which shows a business need of the client which is better handled in ETL.
Regards
Michael