The last known announcement regarding Purchases on Google was made back in 2015. The announcement was also picked up by TechCrunch and Search Engine Land.
But now it seems the closed Alpha is being opened up to retailers on a grander scale. Both retailers and advertisers can submit the request form. It looks as though agencies can implement this at scale with Merchant Center Multi-Client Accounts and AdWords MCCs.
Agencies and firms can also submit individual account IDs for request to enter the Beta. As with most Google programs, we expect the Beta to still be quite limited. Only a select few retailers who meet certain unknown requirements will be able to participate.
As of right now, Purchases on Google requests are open only for US-based retailers. Overall though, this is very exciting news for Google Shopping..