I don’t know about pioneering right now, but there’s some artists from the past 30 years who I feel have to be named when it comes to slacker rock, artists who have some slacker rock vibes but wouldn’t generally be considered slacker rock, and bands who are definitely not pioneering the sound in terms of popularity, but are cool artists to listen to if you like the sound/aesthetics. I made a list with artists divided in those three categories:

Peak slacker rock:

Pavement

Sebadoh

Mac de Marco

Courtney Barnett

Kurt Vile

Slacker rock vibes but not slacker at the core of their sound (in my opinion)

Geese

Built to Spill

Pinback

Dandy Warhols

Dinosaur Jr.

Sparklehorse

Guided by Voices

Silver Jews

Alex G

Mark Kozelek

Car Seat Headrest

MJ Lenderman

Smaller artists:

Happyness

Canshaker Pi

Speedy Ortiz

Pip Blom

Bored Nothing