I don't think it's possible.
Maybe it could match the PS360 numbers, but V was a phenomenon that got the luxury of releasing on very mature 7th gen consoles with massive install bases, multiple bundles, a highly celebrated PC release, HD remasters on hot new consoles, etc.
With 7th gen rapidly dying, and 8th gen unlikely to hit the same numbers by the time GTA6 hits, while 9th gen is almost a certainty to not be in time to get GTA6, I just don't see it. Maybe if it was a very very late gen title in 2019 or 2020 and cross gen with Gen9 and with a PC release shortly thereafter.
A lot of GTAV's crazy numbers were due to multiple buyers. Of the ~50m+ GTAV sales, I bet as many as 25% of them were multiple platform sales to the same person. I know there are some that bought 3 or even 4 versions. Started with 360, 360 RRODed on them (or their PS3 Yloded and they got it for 360), bought it for their PS3 (or a new PS3 bundle), then grabbed a PS4 version when it came out, then grabbed the PC version down the line. Boom, that's 4 sales right there.