Project Upstream, as far as I can tell, is all about consolidating the MLS data. Zillow currently has to take data from hundreds of MLS organizations, in a variety of formats, and consolidate it to put it on Zillow. Once Upstream is completed, they will have one nice data set that includes all the data nationwide in one format. It will be a huge benefit for them, other portals, and large brokers that cover multiple states.
As for individual agents that cover just one area like myself, there are no benefits that I can see. I only need data in the specific area I sell in, and my MLS already provides me this data. There is no benefit for me to have data from areas I am not active in.
In addition, the very specific data for my location might change their format. For example, in our MLS, we have no data field for heating. In Hawaii, no homes have heat. If everything is consolidated, there will now be a heating data field, which might require some updates to Hawaii based websites to make sure that field is excluded.
The same would happen for fields we have that others do not. For example, we have a Leasehold field vs. Fee Simple. Most areas in the United States do not have Leasehold purchases, but when the data is consolidated, we need to keep our Leasehold/Fee Simple field, so others will see that field in the consolidated data.
These are not major changes, but any time the data structure changes, anyone who imports data has to verify their import will keep working.
I know NAR is not investing in Project Upstream to benefit Zillow, however, because Zillow does cover every state, no one will benefit more.