Also I would say moving from the 90s through the early part of the 2000's you're overlooking Industrial, Dubstep, not to mention the changes in country and hip hop that may not have been officially named yet.
For me, industrial started in the 70s with Throbbing Gristle, and Wax Trax records was early 80s. I do think NIN brought something new to the party, but they were pre-1990.
Even though a lot of Dubstep traces back to garage/grime/etc., I'll grant that it qualifies as a genre. But it started pre-2000...I'm looking for something that started in the 2000s and 2010s.
I do think that genres can have relatively sharp dividing lines that are drawn within the space of a year. There are precursors, of course, but often there's a group or scene that lights a fire to the kerosene others already poured. For example the Sex Pistols didn't invent punk, but they opened the floodgates. Kraftwerk didn't invent electronic music, but Autobahn birthed a zillion sub-genres of EDM. And after Bob Marley was "discovered," again, there had been others doing similar music, but post-Marley saw everyone from the Police to Neil Diamond bringing reggae-tinged music into their acts.
I agree that hip-hop and country have evolved in new directions, but to my ears they've been evolutions, not revolutions. You could say the same thing about rock, I guess...the rock of the 50s isn't the rock of today, but there's still a base of guitar, bass, drums, and vocals.
I dunno, I guess I'm just not seeing musicians striking out in any radical new directions. Then again, I'm not either...in many ways I'm not doing traditional rock or EDM, but I'm still building off both genres. I don't think that qualifies as something new, just something different.