Is "Non-IP Data Delivery" (basically SMS but for raw data packets, bound to a pre-defined application server) already a thing in practice?
In theory, you get all the power saving that the cellular network stack has to offer without having to maintain a connection. While on protocol layer NIDD is almost handled like an SMS (paging, connectionless), it is not routed through a telephony core (and hence sloooow). The base station / core will directly forward it to your predefined application server.
It has been heavily advertised, but its support is inconsistent. If you are deploying devices across multiple regions, you likely want them to function the same way everywhere.
In theory, you get all the power saving that the cellular network stack has to offer without having to maintain a connection. While on protocol layer NIDD is almost handled like an SMS (paging, connectionless), it is not routed through a telephony core (and hence sloooow). The base station / core will directly forward it to your predefined application server.