It looks like the Nikon naming convention for Z cameras is different from the F mount DSLRs:
- Single digit for FX models (Z5, Z6 .. Z9), and double digit for DX (Z50)
- higher number represents higher-spec (more professional) model, with Z9 being at the top. This is different from the F cameras where single-digit models (lowest number) were the pro cameras.
- to represent a new generation, the base model number stays the same with suffix added (Z6 -> Z6II). How will that be continued into the future - will we have Z6III, Z6.4, Z6.5 ? 
Either they'll have to add suffixes, or get into HEX mode: Nikon ZA, ZB, ZC, ...
Some deviations from the line were encountered even in early Nikon Digital naming: there is no Nikon D2, they started off with D2H and D2X (and D2Hs/D2Xs)
Anyhow, they cannot have a model name longer than 5 characters, this would alter the in-camera folder naming system (unaltered since the D1):
Folder name is constant 8 characters long, format is nnn + NC_ + model name
You have three characters for the folder progressive number, starting from 100.
You have three padding characters
NC_ (N + C + Underscore), being eventually overlayed by model number
You have the model name (2 to 5 characters), overlapping the padding characters when needed
Examples of folders:
987NC_D3 (folder 987 of a D3 camera)
102NCZ_6 (folder 102 of a Z6 camera)
101NCZ50 (folder 101 of a Z50 camera)
107D5300 (folder 107 of a D5300 camera)
118ND2XS (folder 118 of a D2XS camera)
etc...
Compact models, and waterproof ones (e.g. Coolpix 100-110-120-130-300 AW) will not have the model suffix in the folder name, names are still 8 characters long with a fixed "NIKON" padding, 100NIKON, 101NIKON, ...
Ciao from Massimo
