To me, it depends on the measuring rod one calls "Oldie-ahem, Classic Hits" (and the all too requisite research.)
It may sound strange to hear "Semi-Charmed Life" on a Classic Hits station, but bear in mind that song is nearly 20 years old and it's not exactly the edgiest thing on alternative radio today (or that it ever has been. It sounds awfully mainstream. Even back when it was a current hit.) There's also Hootie & The Blowfish, Matchbox Twenty, The Goo Goo Dolls, Semisonic, Sheryl Crow - basically, the AC playlist of 1999 could be the template for Classic Hits in the coming years if the songs they're currently testing prove solid.
But that's not to say there won't be surprises. The latter half of the '90s saw the return of CHR from the brink and the most accessible pop of that decade. The ugly earlier half is the problem. Aside from Hootie, Madonna and not a whole lot of others, there wasn't very much in the way of mainstream pop. Most of that had been regulated to Adult Contemporary while grunge and hip-hop battled it out with younger listeners. It might be hard to find some compromise now when there wasn't much room for it back then.
But then again, maybe time makes the heart grow fonder. If disco could have a revival every Saturday night in the '90s on AC and Oldies stations, who knows what's in store in the future?
They're treading lightly with the '90s now, but eventually there will be no escaping it. The '90s "Gen-X" stations of a few years ago probably were just cutting it a bit soon when we were still recovering from that insane decade (and there was a LOT to recover from. "Mambo #5", "Nookie" anyone?)