In the case of rumba, alot was invested in that station. Hiring onair staff right away, advertising, sponsoring several events. The station was given more time I think, then say if Philly's 1061 had similar numbers. Even when flip was made, they didn't kill rumba, they just moved it to the am.
With that said, you may notice that nothing has been done with 950 yet. That leads me to believe they're leaving it open to just return as 950espn.
As for a all 90's station. Sounds good to me. 80's stations were popping up everywhere 10 years ago at this time, so it makes sense. Now the nail in the 80's format I feel was everyone went with "the point" consulted format, which wasn't the 80's people grew up with, or heard on MTV, but was really just 80's rock. I think it is for this reason few 80's station survived more then 2 years, while the whole jack format which is heavy 80's has survived in many places including here.
Anyway, my point here is I hope the same mistake isn't made with the 90's format, and they focus on all the music. Not that I would mind if the boy bands of the late 90's was skipped.