Google has updated its title structured data help document for Google Merchant Center to now recommend you add the product's brand name to the title of the product when it's a differentiating factor.
The new recommendation was added here and says:
Add the product’s brand name if it’s a differentiating factor. If you sell products from many different brands and the product's brand is a differentiating characteristic of the product, add the brand name to the product title so that users can understand who makes the product you are selling. Learn more about the brand [brand] attribute.
Here is a screenshot:
This was spotted by Emmanuel Flossie who posted about it on his blog and wrote, "Even though this isn’t a formal violation yet, preparing your titles now will put you ahead of any future enforcement and help improve your product visibility in the short term."
He even made a short video on this:
Forum discussion at LinkedIn.