The office of the Vice President is important for several reasons. First, it is the closest assistant to the president. Due to the president's numerous engagement, the vp is on ground to represent the president at various functions locally and internationally.
An important function though is the provision to step up as Acting President following the absence of the president from office. That ensures there is no vacuum or lacuna created at the highest level of leadership in the country.
Those who drafted the constitution, perhaps did not envisage a situation where a president leaves office for a prolonged period as was the case of Yar'Adua, and now, Buhari. Consequently, the VP is currently performing both the roles of the VP and the President. This shouldn't be so, since both offices have clearly defined roles.
Here are some fundamental issues: in the situation where the acting president travels out of the country on official engagements or a good example was when PYO visited his superior in London, who takes charge on his behalf? Or if the acting president falls sick and has to seek for medical treatment, who takes over as acting president? Or ultimately, if he dies while acting, and whereas the president is not physically fit to resume office, who then takes over as acting president?
I guess these are fundamental issues that should be addressed constitutionally.
I suggest a new office of deputy vice president be created. The Deputy vice president will function as a Minister. But once the Vp steps up to be acting president, the deputy vp steps up to be acting vice president. Or if the vp eventually becomes president, the acting dvp assumes the office of the vp.
I think a decisive action should be taken in this regard. We shouldn't wait for the unimaginable to happen and then scamper to evoke another unlawful doctrine of necessity.

Nice post.I also read your signature without turning my phone upside down.