My dayjob of several years had me working as a produce stocker at Wal-Mart, and during that time, an idea that kept running through my head was a "Wal-Mart simulator", where you would build and run your own big-box store, deciding its layout, hiring employees (who each have unique skills and personalities), and deciding whether to be a benevolent boss who makes sure the people you employ are happy and fulfilled or a dedicated capitalist who grinds every penny possible out of everyone that comes under their roof. To give the game an extra flair (and show just what I think about big business and stock traders), all of the richest and most powerful players in the setting, including yourself, are literal demons. You've come up from hell to engage in the most heinous of professions - retail management, your secretary is a succubus, and the game's stock trading system is framed as you selling your soul to more powerful devils.
There are many reasons why Retail Overlord would be the smartest decision for RJS's first game. Retail Overlord would be built on largely the same code base as Mighty Miners, since both are games that mainly consist of managing semi-autonomous units on a grid-based map, so we already have an engine ready to go that would only need minor tweaking. Simulator games like Prison Architect and Two Point Hospital set a precedent for games of this type having demand and meeting with moderate success. And finally, the aesthetic of a modern retail company run by business suits who are also actual demons is a concept practically tailor-made for the talents of the artist we already have working on Mighty Miners.