Pretty much every Linux/Samba-based NAS on the market has the same policy limitations as a desktop Linux installation.
Plus, the mailslot interface is a very important part of the protocol. It's how networked users have been able to communicate with one another for quite a long time, without needing third-party software, which also provides an interface for applications to also do so across machines. The reason it was likely never fully implemented on Linux is because there is no reasonable way to implement it, given the lack of any kind of standardization (particularly in the GUI). Literally the only thing available, after 20 years, is Linpopup, which basically doesn't really even work anymore anyway. And there's no proper interface to take advantage of mailslot functionality to make anything better. RealPopup is a very good WinPopup replacement on Windows, with quite a bit of configurability, but it's completely unable to communicate with a Samba-based machine in its native mode.
So, what options does that leave us with? 1) A cross-platform internet-reliant instant messenger service, full of ads and spam and regular updates. 2) A local server-based chat application, requiring configuration of both a server and clients, and also requiring aforementioned server which severs all network communications if that machine is down. 3) Something Bonjour-based, all of which are typically extremely bloated and require installing garbage Apple software on a PC to communicate.
That means all of the Linux-based machines I use have no way of communicating with Windows users on the network, meaning I have to always have a Windows PC as well, because there is no reasonable alternative.