I have similar thoughts. I am slowly selling off my way too large stash of bicycles.
I have sold my two Sam frames on this site and also have an original model (quick releases, not through bolts) fat tired Crust Scapegoat that I was considering posting here when the time came. I basically feel that is OK as Crust is Riv-adjacent, even if the Scapegoat not very Riv-ish, although maybe a little hilli bike-ish.
I also have a Scott Sub-10 that actually has a lot of parts that I bought from Riv on it (Brooks saddle, SKS mud flaps, Little Big Ben Tires), but I would feel less OK with posting it here. It is in a certain way more Riv-ish in set-up - fully fendered, fully racked, dyno-hubbed, upright, but it has aluminum frame, belt drive, disc brakes so I would be less comfortable trying to sell it here.
And then there is the no-name fully lugged, nickel plated, chrome-moly single speed with the Resurrectio decals - I would feel Ok trying to sell it here.
Not sure what my criteria actually is.
Note that none of these bikes are for sale yet or any time soon and may never be and I would never remember if anyone was interested now, once the time comes to actually sell.
Laing