I don't know of any easy way to do this. If you need it to be in Illustrator, then it needs to be built in Illustrator.
There is no suitable way.
You could TRY to open PDFs but the chances of that being more successful than starting from scratch are slim.
Since it isn't a question of best practice, or any practice at all really, it may be worth letting us know why you find yourself wanting to do that - what problem are you trying to solve? Looking at the big picture, there may be a better way.
I know this isn't a preferred workflow, but this is needed to take data merge artwork and supply to clients in Illustrator.
The indesign workflow for the data management is so much easier to control with the amount of variables i have, so the conversion back to Illustrator is the minor irritation in the scheme of things.