I'm happy to just use Illustrator for this purpose.
However, just to give a real-world example (checking back into this 5 years later) - while I'm thinking about it - here it is.
I have this illustrator friend who is a BIT stubborn. He wouldn't draw with a Wacom - or anything digital, but I'm using the illustrations as SVG and controlling their color in a web document with CSS (Example). So - for that reason, I can't just ink it. It wouldn't maintain his style. He also wouldn't like someone else to go over his drawing. Now, 2020 - he's finally got an iPad - and he tried pro-create - but now wont try anything else (clearly - fixing him - would be easier than adding the 'trace to object' type feature). So, from pro-create - he's not giving me vector. It spits out layers of png - and then I have to put those in illustrator + programmatically trace them + and then put them in layers + and manually amend the SVG code for my CSS. I just wanted a real use case somewhere in this thread.
I understand that it's a complex process - but I also think that there's a use-case for a less complex version. How many people are image tracing things other than line drawings? Would 1 color tracing be any different. I can just use illustrator. Not a huge problem for me. I'll take some perspective tools over this any day.