I'm not sure there were ever any SERIOUS plans; I think they were more putting out feelers at the time that, if the movie was successful, it may lead to a spin-off. But yeah, the fact that Michelle Yeoh's character didn't even get that is surprising, as it felt like they were setting her up for her own spin-off.
Thinking back, I really don't remember much about the Dalton Bond movies. I remember Felix being fed to a shark, Bond going rogue, the 18-wheeler chase and the drug dealer, and Dalton parachuting onto a yacht and using the phone to call in before making time with the woman on the boat, though that was in the other Dalton movie. And that's it. Yeah, Brosnan Bond's are a product of their time, but at least they were more memorable.