Some tests:

• Associate icon with job name:
  
• Grey out the bar when canceling and change job name to "Canceling...":
  

Glad to see someone working on this :)

For the design, I'd suggest following the mockups from @venomgfx for the widget redesign as this is the direction we're heading to.

We should get rid of the ghetto rendering mouse thing

sorry did not work but you know what i mean

Black text on dark gray is generally not a good idea, rest seems alright to me.

Is it possible to add an option (maybe that can be switched off/on in the user preferences) of render canceling confirmation prompt? Similar to File > New (Reload startup file). Because now there is the hover over tooltip with the render remaining/elapsed time there are more reasons to be with the cursor in that area and misclicking.

I'd rather not add user preferences for this, it's not really solving the issue properly. It might be a good idea to always show a confirmation prompt when the job has been running for a certain amount of time, perhaps after 1 minute. Or is that too inconsistent?

In T42004#353920, @Brecht Van Lommel (brecht) wrote:

I'd rather not add user preferences for this, it's not really solving the issue properly. It might be a good idea to always show a confirmation prompt when the job has been running for a certain amount of time, perhaps after 1 minute. Or is that too inconsistent?

Yeah, maybe as a part of a general approach of dealing with canceling current operation that takes time to compute or warning about an operation that couldn't be revoked/undone or continued etc. would a much better idea. Like blender locking up after a modifier is selected by mistake (like skin modifier on a huge mesh happened to me once too). That would make the system consistent. But, in my naive opinion that's not so trivial, and most likely a ToDo maybe for 2.8. :)