Over on USK which is the German game rating board Gem Stadia and Bahlor on Reddit have both noticed that Hotline Miami and Hotline Miami 2: Wrong Number have been listed for Stadia. As we say with all games getting rated by games ratings board this is an indication that they will come but does not guarantee they will.
If I was to speculate I believe we would get the Hotline Miami Collection to Stadia which combines both games. The games are highly popular and have a fan base. They are violent which may not all.