Brief title for your desired feature:
Inline Smart Object Editting
How would you like the feature to work?
Make Smart Objects editable without double clicking them. Add a drop down arrow so that you can see all of the layers (just like folders). Then, you can edit right there. If you have multiple instances of the smart object, you can watch them all update together.
Why is this feature important to you?
For one, I could edit more quickly. Also, with this functionality I would be able to edit projects in an 'environment'. If I'm making a backdrop for a stage (which I do), I can take a picture of the stage, and work on the project within the actual stage, and make a better composition that is more cohesive with the surroundings. When you're done, you can just export the smart object, it's already got the right dpi, dimensions, color mode.... it's done. I could paint light shadows in the main canvas over areas that are in the dark, so that I automatically make those colors brighter in the 'smart object' (that feels like a folder) without even thinking. I could place objects in front of the smart object that will be covered by a speaker or a person. You could also use it for product design, to create a label directly on a bottle. Or if you want to create entire projects in one psd, where you've got an empty business card, dvd, dvd box, poster, all in one file and in one fell swoop you finish the whole job. I could see it used for billboard designs, and many other projects.
BTW, you could make two modes for Smart Objects. When you first place/create a smart object, it is in normal mode. But, as soon as you skew it (to give it perspective, or just to squash it), it enters perspective mode. When you choose the brush tool and paint on a layer in a smart object in 'perspective' mode, you see a light green square on top of the smart object that represents the smart object's boundaries if it were flat. As you paint in the light green boundaries, you see the edits happening in the skewed perspective of the smart object. That could be very handy for many different scenarios. Same with the type tool and every other tool.