I reckon this isn't too far off, as the AIM-132 has demonstrated a lock on after launch ability: firing at a target behind the launch aircraft. If modified this could be mounted such a way that allows the sub to launch while staying completely submerged, and the missile locks after breaching the surface

All that would be required is a weapon that can do a LOAL so that once launched and into the air, the missile then does a 360 degree orbit, allowing its sensor package to "map" likely targets. At that point it then determines its target, turns to the proper bearing, locks and accelerates to terminus.

While the digital battlefield is good, it is important to remember that digital links can be severed.