To map signals, you'd have to be able to identify what synapses contain what memories. You can bet your life everyone is different and is observed differently.

Although by monitoring someone doing a specific activity, like moving a limb - you could potentially mimick this person's action. So who knows, maybe we'll calibrate such a device using this method. But it may be difficult to target this part of the brain specifically.

Considering our smart phones and apps are so jam full of bugs, I don't hold much hope for such technology. Imagine the sort of bugs you could observe with such tech, super invasive bugs too.