Okay but hear me out.
Nintendo could add an endless mode to Salmon Run in Splatoon 4 where after each wave players can pick from a few options for ability or weapon boosts the same way color chips work in Side Order. I think this is the most likely way they would implement abilities into Salmon Run. It also fits with the lore of the salmonids becoming more and more aggressive as time passes.
Who wouldn't want a Build-your-own-Grizzco-weapon™ mode?