You can get L2 charging at many RV parks. It isn’t what I would consider very practical though.

>If charging time is linear

Three phase 16-25A outlets are available (common in buildings/houses) in Europe (230V each phase to neutral, 400V phase to phase). Charging Li-Ion is not a linear process at all, but at so low power (0.02C, compared to the target's battery one) it'd be, as it'd be limited by the source instead.

Most RV parks have 40-50 amps available, which makes overnight charging more practical

It's unlikely they will be able to supply that much current if there are many participants.

Yeah, they'd need to add EVSEs with load sharing. Fortunately, that'd be cost effective if there were many customers clamoring for it.