This line is not present in URA's Concept Plan 2022, so there were murmurs about how it would pan out. It is likely in very early stages.
The alignment and the station locations are not difficult to make out. In fact, I would believe they need this line sooner than later, starting with the northern sections, as the road network around Yishun East is showing signs of saturation.
@camrysfe Good analysis there, but this line is unique in that the stops between interchanges can be quite far. Out of Simpang area going southwards, I can see Seletar, Fernvale (out-of-station transfer), Lorong Chuan, Boon Keng before the interchanges get closer. The line would probably need to run until Lorong Chuan before demand is somewhat healthy, but it lacks 3-line interchanges.
Any announcements, if confirmed, should be made in 2024 onwards after CRL3 is announced, with the first stage opening 10 years later.