You guys really aren’t adding standardizedProductType to the rest api? It’s just a simple field!?! Why hate on the rest api users like that? 
According to a Shopify Staff, they’re still working on the REST version but no ETA yet as far as I’m aware.
That was almost a year ago though and I do hope this is still on their roadmap.
Source here: https://community.shopify.com/post/1523058