Lets not anoint Mayer until she does something more than just faffing about and weakening user experience.
Microsoft isn't agile, and politics in the company won't make it as easy for a "Mayer" to come in and whip it in to order.
Do they really want Mayer anyways? It seems like that while she has given them more publicity she hasn't seemed to do very much that actually matters. Sure they made a new logo and bought Tumblr, neither were very good ideas.
Microsoft does have a big PR problem. The brand has lost its association with innovation, coolness, etc. That does not mean though the company itself is lacking in those attributes. From that perspective yes they do need a Mayer. Although it will be interesting to see if it results into empty hopes like what has resulted in Mayer's tenure so far.