Airdrop is very nice when it works. Modern apple hardware has a second wifi modem for an ad-hoc connection so it can be faster than normal wifi as well.
But Apple only.. makes it much less useful, even for “Apple people”.
Technically yes, it's a virtual device, but not all wifi hardware is capable of running two networks at the same time, Apple carefully selected the "usual" hardware to support this.
Almost all Wi-Fi chipsets released in the last couple of years support this.
Many Windows and Android devices have been able to share a Wi-Fi network with other devices over another SSID, for example.
The only thing that's complicated is if a device needs to be a 802.11 station on one frequency/channel, and a host or P2P device on another, but that's almost always avoidable.
Everything else can be done purely in firmware or software.
Has it ever been reverse engineered and reimplemented?
I use apple's IP audio streaming protocol (forget what it's called, air-something) to play music over a couple of edifier-brand speakers from a Linux desktop which is running pipewire's FOSS implementation of the protocol. I don't even buy apple products but i ended up using it because there's no way to just netcat samples onto these things.
Do you have any sources for that? As far as I know, it's just time-sharing the same baseband and hardware used for regular infrastructure-mode Wi-Fi.