This could be possible because AP is the first to check data sent by client if proper passphrase was used. Probably such feature could be implemented to some extent where AP could check against fixed set of passphrases and take one action or another.

I would like to be able to assign a VLAN based on the PSK used. This would be useful in hotel/apartment/condos where each unit has its own passphrase. It would for a single SSID (from every AP on the property) and allow for private Wi-Fi without using MAC addresses or RADIUS or landing pages.

You can do this standards-based when using WPA2-EAP. Almost every client supports it.

You can always buy an AP that supports it!
You will never find all features in all possible devices at all price levels.

You can always buy an AP that supports it!
You will never find all features in all possible devices at all price levels.

The problem isn't the AP (we're talking about Mikrotik - they all support EAP), it's the client devices. Not all support EAP, especially consumer devices. The example above of an apartment building is a relevant example where EAP would be ineffective.

Yes, devices like Chromecast and printers don't support EAP.

I too in the past have wished for password based VLAN assignment without using RADIUS. In the end I have done it using the hotspot, CAPSMAN and some script fu - as in hotspot logins get put on their own VLAN. It works very well considering there is no RADIUS involved. Using hotspot of course implies there is no Wifi encryption (until WPA3 comes along).

MIKROTIK_WIRELESS_PSK

Basically, I want user to be in the same VLAN as the chromecast, so they can cast the content in the hotel room TV.
I only want the guest to to access the chromecast in their room. The only way I can make this happen is if the guest and the chromecast are in the same VLAN.

... but unfortunately it is impossible ... or send passphrase to RADIUS server (passphrase is not known).

[root@pfSense.test.home.arpa]/usr/local/etc/raddb: cat users.PSK
# Mikrotik Mac Auth and dyn. VLAN
# Mac Format XXXX:XXXX:XXXX
#
# check any User 
DEFAULT Cleartext-Password := "%{User-Name}"
#assign VLAN per PPSK

switch %MIKROTIK_WIRELESS_PSK  {
    case VLAN1_PPSK {
        Tunnel-Type = VLAN,
        Tunnel-Medium-Type = IEEE-802,
        Mikrotik-Wireless-VLANID := 20,
        Mikrotik-Wireless-VLANID-Type := 0,
        Mikrotik-Wireless-Comment = "USER_01_DEVICE"
    }
   case VLAN2_PPSK {
        Tunnel-Type = VLAN,
        Tunnel-Medium-Type = IEEE-802,
        Mikrotik-Wireless-VLANID := 10,
        Mikrotik-Wireless-VLANID-Type := 0,
        Mikrotik-Wireless-Comment = "USER_01_DEVICE"
    }
   case {
        Tunnel-Type = VLAN,
        Tunnel-Medium-Type = IEEE-802,
        Mikrotik-Wireless-VLANID := 99,
        Mikrotik-Wireless-VLANID-Type := 0,
        Mikrotik-Wireless-Comment = "UNTRUSTED_DEVICE"
    }
}