Nothing confirmed but if it happens it won't be soon. In March the creator said "please wait a little longer for season 3." Tbh I think seeing A Certain Scientific Accelerator get an anime adaptation soon would be more likely.
at this rate an anime of the forgetin' virtual-on crossover is more likely because they're making a game out of that
instead of an actual loving virtual-on game
god loving dammit sega/dengeki
give us an actual virtual-on
give us an actual index S3
everyone will be happy