Pros and Cons of using Unity WEBGL for a full blown admin portal ( non searchable websites)

I am unable to find the actual disadvantages of using WEBGL or Unity WEBGL as a matter of fact for building websites that can be used as admin portal. As I understand, WEBGL for SEO friendly websites is a bad idea. What I am concerned if the need for SEO need not be there. Then ? I would like to know the problems other than SEO. Like Security ? ORM ? and other stuff that a websites framework in PHP or node.js like SAILS, YII, ZEND deploy.

Its easier to build and customize UI and navigation things in UNITY than using web templates.

So I would like to know the Pros and Cons in comparison to what these frameworks offer.