The point of the studies is to determine the upgrades required to the transmission system to ensure stability and reliability (prevent cascading failures)
Also we're working towards a system where demand can be controlled. Think your electric car stops charging or your air conditioner kicks off for 10 minutes when there is a problem.
Batteries exist in a different economic regime than rate payers. Where the price per megawatt varies by 2X or more. Which makes it easier for batteries to make money be arbitrage. As in buy power at 10am for $40/MWH, sell it at 7pm the same day for $80/MWH.
So making $40/MWH * 100 MWH/day = $4000 per day * 365 day/yr = 1.4 million revenue per year. Not enough to pay back $100 million.
Like you said The economics of it keep improving though Imp
The study might show that the upgrades required to inject power at a project location and maintain system stability and reliability are too costly and the project can’t proceed as proposed.
The studies are usually performed in the order that the requests are received.
Project proponents are often unaware of where on the grid the most cost effective interconnections are for a given project size.
The feedback loop between proponents and utility could be tightened up if the utility would publish a map showing available capacity or cost to upgrade vs new capacity for different locations on the grid.
That is one way the utility could meet the demand to perform the studies faster with the same number of quants.