AJ McLean wants to capitalize on a viral mashup of an old Backstreet Boys hit and a new Taylor Swift song ... and he's asking Taylor if she wants to perform with his band in Las Vegas ... telling us such a collab would "break the planet."

We got AJ at LAX on Tuesday and our photog asked him about potentially working with Taylor ... who has indicated she likes the "Elizabeth Taylor" and "Everybody" mix.

AJ posted a video on Instagram with the mashup, showing him lip synching ... and Taylor commented, "OH HI AJ OH MY GOD."

BSB shows at The Sphere in Las Vegas have been a huge hit and folks are clamoring for Taylor to join them onstage to perform the remix ... and AJ tells us it would be epic. Splash News

Taylor's a BSB fan herself and AJ says she needs to come check out a show f

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