Well, if the sidekick is an incorporeal being from a digital world, their powers are basically going to be "super hacking." They'd be able to access data networks, control drones, stuff like that. Maybe you could say that they can screw with the electric signals in the brain, given them a limited/specific kind of mind control. But without a body, options for powers are going to be kinda limited. I'll be honest, I like the idea of a digital being in Vic's supporting cast but the concept is likely too limited for a sidekick.
If the sidekick has a physical body and is from the Nightshine....you could do any number of things. Pretty much every troupe from 80's era fiction seems viable for the Nightshine. Weaponized sound/music seems a little on the nose to me but would most certainly be fitting. We've seen (in TTGO! Nightshine) cybernetics (though not as extensive or powerful as Vic's), shape shifting, some crazy Transformers stuff, anime-style fighting and super jumping and giant guns and robot swords.....you could have the sidekick with nearly any power, but it should be something big and flashy and ridiculous; the "louder" the better. I've got a fondness for the "unifying fields" power; manipulating gravity and the electromagnetic spectrum and the nuclear forces.....tons and tons of stuff you can do there, yet it's a powerset almost nobody has. I think if the sidekick is from the Nightshine, their specific power/s isn't as important as ensuring the overall aesthetic.
I don't necessarily disagree with you, and I do think that the effort needs to be put on Vic and establishing his "post-angst" status quo and setting more than forcing a sidekick into things. But I think if the goal is to establish a firm mythos around Vic then it's never too early to start laying the groundwork for the sidekick. You could introduce the character into Vic's setting without them immediately going into the sidekick role, which would give readers time to get familiar with the new addition to the cast and get a feel for the character.
And if we're treating Vic's shift to the JLA as him "hitting the big pro leagues" then getting saddled with a sidekick, just as his career is taking off and he's starting to sell some Nikes (to stick with the metaphor), would potentially add some quality conflict and drama.