The opposite of bardcore

I thought of two words:

Remake (Idoceonline)

a record or film that has the same music or story as one that was made before

cover or cover version (Free Dictionary)

A recording or performance of a song that was previously recorded or made popular by another

I would add the interesting, but a little bit general reinterpretation about which I found a sentence that reminded me of your request, although it does not perfectly correspond to it (Vocabulary.com):

If you see a rap version of Shakespeare's "Romeo and Juliet," that is a reinterpretation.

Edit: These words are not antonyms of "bardcore", since they refer to remaking any previous song, be it modern or old.

On Wikipedia you will find this sentence

In popular music, a cover version, remake, cover song, revival, or simply cover, is a new performance or recording by someone other than the original artist or composer of a song.

The word that caught my eye was revival. MWebster defines it as

a new presentation or publication of something old

However, it seems to be used more for whole trends of music, not for one particular song. So there are expressions like folk revival, blues revival, rock revival or even revival(ist) band.

So, I am afraid that if you want to be precise, one single word will not do. You would need to say a rock revival song or blues revival song, etc. - adding the name of the particular music trend and the word song (so as to differentiate it from the revival of a whole trend revival).

For more information you can check this similar question on the SE Music Fans site, it might help you to pin down your term.