Expanding on that, we could have three stages for TW and three more for Ranked. The ranked stages would rotate as SZ the first eight, TC the next eight and RM the last eight. That way, the competitive people can enjoy the night-time spectacle while the casuals get to splat away without having to deal with tons of salt.I would like to see Splat Zones in a Splatfest at some point. Not necessarily as a full replacement for Turf Wars, but rather in rotation with Turf Wars. Maybe it could start with Turf Wars, switch out with Splat Zones 8 hours in, and then go back to Turf Wars for the last 8 hours.
The other two modes I'm less sure of, but I can't think of a good reason to exclude them.
As for your concern, why not just use the post-20 levelling system?I would love it, but it would most likely take longer to level up, as ranked battles can be up to five minutes long as opposed to the usual three for turf.