A new concept I have been hammering out that I have posted about before elsewhere. Let me know what you think.

Is able to muster the energy to do:

Ej - Anything (Whatever they want or desire to do + Whatever is required of them that they may not desire or want to do)
Ep - Whatever they want or desire to do (Cannot do whatever is required of them that they may not desire or want to do)
Ij - Whatever is required of them that they may not desire or want to do (Cannot easily find the energy to do what they want to do) [Think Obligation]
Ip - Nothing (Cannot do whatever they want or desire to do, and cannot do whatever is required of them that they may not desire or want to do)

Obviously any type can do anything, but the energy levels of the temperaments represent how easily they can muster energy to do either whatever they want or what is required of them that they do not necessarily want or desire (this isn't black and white, either, I believe this would exist on an individual spectrum).

Ej - Energy is easy to muster for everything
Ep - Energy is easy to muster for whatever is wanted or desired personally
Ij - Energy is easy (or moderate, introtims tend toward less energy) to muster when there is a sense of obligation or responsibility
Ip - Energy is not able to be mustered easily.