The author sets out his future growth assumptions, then summarises them as follows:
"A plausible hypothesis is that total passenger journeys will recover to about 80% of pre-Covid levels and (due to the number of short-distance journeys) about 75% of passenger miles. The loss of high value business and long-distance commuter volumes could well mean that total passenger revenue recovers to only about 70% of previous levels. Growth will, no doubt, resume, but from a lower base - the growth curve will move significantly to the right and may well display a flatter angle."
I recommend reading the article in full to get a better understanding of the proposals than can be conveyed on this forum. The final paragraph is worth quoting in full:
"The key to all of this is a revised timetable that provides the right amount of capacity and an attractive service to encourage growth, but at an affordable cost. A resource-led train plan, with diagrammers determining the optimum way of meeting a broad service specification, would enable the number of units and staff required to be established. Now is not too soon to start that exercise."
[Julian Worth, Modern Railways January 2021 edition, pages 82 - 83].