The associated report does have more details whether or not you agree with them. The article is more of a summary.

re: demand projections
"the carbon neutral and carbon negative scenarios were required to meet the same demand for energy services, for daily life and industrial production as the business as usual reference case from the EIA's Annual Energy Outlook and used its assumptions for population, for GDP and industrial production. So that's very much nothing changes in the world except for the energy system... kind of a view. And the modeling only allows technologies that are commercial today or that have been demonstrated at large pilot scale today. So in effect, I think that really sets a pretty high bar because in reality, I would expect a number of those things to change over the next 30 years. For example, I would expect probably lower population growth than EIA projects and considerably lower demand for energy services and industrial production as a result of a slowing economy. And I would have said that before we have the added effects of the pandemic. "
re:feasibility
"I think at it's core backcasting is about trying to understand what's entailed in the physical transformation. So the legacy of this work is in that discussion about feeling like that's the analysis that's needed. Not necessarily understanding what does a carbon tax do on the margin or what to other approaches do sort of in the short term and in the macroeconomic system. But really understanding how many more widgets do we need and how quickly do they need to be deployed if you don't want to do early retirement. So that context of the questions we're trying to answer really sets up the insights that come from backcasting. So one of the things we think a lot about is stock turnover. So sort of one of our modeling principles is that we don't do early retirement of any resources except for potentially an electricity supply. So for things like light-duty vehicles or industrial boilers, we really need to understand how long do those resources typically stay online? And that means if it's a 15-year turnover rate for something like a furnace or maybe it's a 30-year turnover rate for something like an industrial boiler."

re:cost
"And we find that that case at a net cost of 0.4 percent of GDP in 2050 is able to achieve carbon neutrality. So that 0.4 percent of GDP in 2050 over the reference case, it really represents some major shifts in terms of monetary flows. So we're spending $950 billion on efficiency, new supply for low carbon solutions, and we're saving $800 billion on fossil fuels that are no longer being burned. So our analysis really only looks at the energy costs for the total system for that transition. We're not accounting for things like co-benefits or economic benefits from the avoided damage of climate change or other potential impacts, as well as potential health or environmental benefits. That total energy spending declines from about five percent of GDP for the energy system today to around four percent in 2050. "
-quotes from podcast linked in first article

https://www.unsdsn.org/Zero-Carbon-Action-Plan

https://irp-cdn.multiscreensite.com/6f2c9f57/files/uploaded/...