Debug into external libraries
Single-step through the source code of libraries that a LINQPad query references. This would require the .pdb files and source code to be available on the local machine.
Tom L commented
This would be amazing. We have a huge VS solution at work and I generally write and debug new code in linqpad and then move it into one of my projects. Being able to debug into one of our libraries would be a godsend.