Okay so the thing is, while potentially flexible, Shadowdark is a very focused game. The way the rules are laid out is for a specific type of experience. Light character creation, involved real time crawling/exploration with round robin intiative and random encounters that play out quickly. Inventory Management, Survival Rules and Downtime is very light, streamlined.
I think it would be very imprecise to claim that Shadowdark is basically just a better version of TSR anything, it is very much its own thing that innovates upon TSR/WotC design.
Also I have to concur with Bae'zel, just because Dionne has not written it, doesn't mean people aren't free to build upon it, swap out statblocks or set it within a different setting. But as is, the rules the way they are now are written to specifically support the bread and butter dnd fantasy