I would love to find a copy of the report KSL is quoting here, because it is nonsensical garbage.
The Airport Master Plan prepared by RS&H in November of 2020 and updated
May of 2022 is at complete odds with what is being said in the KSL article.
Here is a chart with RS&H's findings about facility requirements.

By their estimates Concourse C likely wont be needed until between 2057 and 2062. Note that Concourse D wont be needed until
2077!
They elaborate, pointing out that the airfield (with improvements) will only be able to support enough daily traffic for Concourse C.
This paragraph is the real icing on the factual cake.

The airspace, airfield, and terminal infrastructure would not be able to support a Concourse D
which would bring SLC up to the size of ATL. Furthermore they point out that even if Concourse D is
EVER needed, they can still develop the land it would occupy because any possible need is so far out that
new structures would live out their functional lives before Concourse D is needed. The existing terminal will have outlived it's design life before Concourse D is needed.
I don't have a clue where Salt Lake City is getting their numbers or the delusion that they'll need Concourse D so soon. The master plan makes it clear that we'll all be in assisted living or 6 feet under before SLC could possibly need 4 concourses. I see a future of growth for SLC but never will we need an airport the size of ATL.
EDIT: I found the document that was presented to the City Council. It is the same document I quoted and linked earlier. Still no idea how they are saying Concourse D could happen in the 2040's when the damn document they are citing says 2057 at the earliest for
Concourse C. They also ignore the fact that the airspace
can not accommodate that much traffic.