SAP MM has a really good future. The SAP technology is going to stay in the market for at least the subsequent thirty years at the current state and it is still growing. Among the various modules, it's the functional modules like mm, SD, etc which are in great demand. MM module is in use in most of the SAP projects as the material is one of the basic needs of most of the companies using SAP. You can learn a lot of functional modules like sd, QM or technical modules like SAP ABAP, Basis, etc to add to your market value. Techno functional consultants are among the best paid in the SAP business. So, SAP mm has a very good future scope.
Quick video for you to get the gist of SAP MM if you are new to it: