I've done 1 RTW in 8 days elapsed, with 2 nights in a hotel (the rest sleeping on airplanes). This was for work, and not a MR, so no attempt to maximize but it was over 50K base miles. Also very tired at the end of the 8 days, despite flying in F with a nice bed on most flights. So it is possible. As for mileage, you can make EXP on AA with a single DONE4 (but much easier with a DONE5). Whether it is worth it is a matter of opinion. There are more cost-effective ways to earn miles and status, however none will get you to top-tier in 8 days elapsed.