Some GPS's have battery supported RTC's built in, making them a valid time source even before a fix is acquired.
It should be possible to optionally make use of this capability by using the time supplied by the GPS's RTC in circumstances where it is needed.
Example hardware:
Situation that warrants use of this capability;
Raspberry Pi or other devices lacking hwclock, when it is not consistently powered, and has no or limited network connectivity, especially when operating in a somewhat shielded location where it is difficult or impossible to get a GPS fix.
I'm looking specifically at commit 0d5dd8f4b567a628a65b7be1110386b086d59f63
or line 1516 in release 3.16.