According to the comments of a Google engineer on the code in the open source Android project, Google is working on a new "Pixel 2019". Well, of course, Google is working on new smartphones for this year. But what's interesting, like XDA Developers discovered over the weekend, is that the new phone should have better support for dual SIM cards. This could mean that Google Pixel 4 could work better on two different networks of mobile carriers at the same time, instead of having only one enabled and the other disabled (and forcing to choose which one it is).
In fact, the dual SIM functionality is active "dogfooding" on Google Pixel 3 at this time, which means that Google is already testing it internally on a phone that you could use today. We know this thanks to the comment of the Google engineer, which you can read below, but first, here are some contexts. Google Pixel 2 and 3 have both a physical SIM card slot and an eSIM, but both can not be active at the same time. This is in direct opposition to how the latest iPhone work, which are able to receive calls and messages from both networks.
Other Android phones can do similar tricks on multiple networks, and this feature is actually quite important for some people. In some regions of the world it is normal to quickly switch from one network to another to achieve the best data transmission speed and is also an advantage for people who travel a lot. The inability of Pixel 3 to have two active SIMs is a hassle for many people.
This value Boolean will be set to true on 2019 devices by default.
Boolean is needed to differentiate 2018 Pixels (which has 2 SIM cards, but dual SIM functionality is limited to dog food) from 2019 Pixels (which will have dual SIM capabilities).
The flag will be updated via ether for dog food.
As for the bug you mentioned. In general, some devices will be single SIM, even if they contain two SIM cards, such as the Pixel 2018 case and this is a valid configuration.
The code here is essentially an engineer who is working on how Android itself will know if a phone supports dual SIM. XDA also emphasizes something you should know: there is more than one way to manage dual-SIM capabilities. One is "Dual SIM Dual Active" (DSDA) in which both SIM cards are active and can be used for calls, text and data. The other is "Dual SIM Dual Standby" (DSDS) in which the secondary SIM can only receive calls and texts, but is not fully active.
The iPhone uses DSDS and presumably this is what will come on Google Pixel 4. If the dual-SIM feature for current Pixels will ever get through Google's internal tests on your Pixel 3 is an open question. If I were Google, however, I would work hard to make sure that it works with Google Pixel Lite, because it will be more suitable for markets like India, where the double SIM is more appreciated.