A sphere is a perfectly round and flawless object, but the universe is neither. As space expands, whether inside or outside the Hubble Sphere, some may expand at different rates, as there are some points moving further from our location than the speed of light, and others do not.

Having differently expanding regions would not present itself as a sphere as much as a more fluid or waved object. A more similar object would be a bubble, as it may keep a relatively spherical shape, it is more fluid and effected by the forces around it. Additionally, bubbles are subject to changes in size, unlike the idea of a sphere, which is more finite and not an apt measurement when referring to the vast infinite mysteries of space. 

I propose renaming the Hubble Sphere to the Hubble Bubble. Aside from my above previously stated opinion, the current name was an egregiously missed opportunity.