Nothing too niche or topical. Has to have some sort of timeless quality, meaningful lyrics and emotional resonance. Not a "fad" genre, a sea shantey won't do (yes its centuries of tradition but in it's old form it isn't mainstream). Cultural impact which means it will moat likely be from your mainstream artists, taylor swift, kanye west, maybe billie eilish gets there. I also think it's probably going to be more women defining an era of music than ever before.

Added advantages, either something that was early in a musical tradition or helped it peak, we've seen this with classics in the moat recent big genre, rap.

As for the tiktok songs. We don't know how internet virality affects the legacy of these songs. A lot of the earbugs are shallow short bits. I'm going to ignore those, otherwise I think some of the smarter songs will maybe be appreciated a little while later too.

So my list:

• Royals by lorde
• Rolling in the deep by adele
• Runaway by Kanye
• Sign of the times by harry styles
• Hotline Bling by drake, i'm 50/50 on this one
• All Too Well/ Blank Space by Taylor Swift
• Alright by Kendrick Lamar
• Formation by Beyonce
• Teenage Dream by Katy Perry
• Chandlier by Sia
• Uptown Funk Mark Ronson 50/50
• Let It Happen by Tame Impala
• Nights by Frank Ocean

I think a couple of these are pre 2014 tho. But are within the last 15 for sure.