With the possibility of this new update, the Pixel 4 would have to have two active SIMs. However, it is not possible to make a call or text for the time being. This is similar to howand other Android phones operate.
Having a dual SIM is beneficial to those who have more or less than one number (a personal and a work number, for example). If this rumor pans out – and keep in mind it's just a rumor at this point; Google did not reply to a request for comment – the updated SIM capabilities would even offer more flexibility to Pixel users.
For more info, read why you should.