Some VFB improvements are planned, but I don't think "photoshop inside Corona VFB" is viable. :)
"change colors, brightness, etc" - this is already possible using the tone mapping / post processing
"control the render elements inside VFB" - can you explain what exactly you mean here? how would you like to control them?
If you have some improvement ideas for the VFB - could you please list them one by one and be as specific as possible?