And even commercial broadband services.... In full disclosure I worked as a supplier to implement MPTCP on the CPE for BT at the launch of their service (time marker 1:48 starting point) : https://youtu.be/eMKAFWy6940
MPTCP has been in use at massive scale on iOS for years now for core Apple services and any iOS application that uses Network.framework can leverage it too.
Say have eth, wifi(2.4+5Ghz+6Ghz) and cellular network, you may want to use them fully all together, there's a way for mptcp to shine;
or you have multiple proxies, and wants to improve reliability, you can also use mptcp.