Based on their press release from today the bonus will be on top of all miles accrued. There is an example for FRA - NYC in biz.
"an M&M customer with status will get 19,254 miles instead of 15,404 as it is now" the 3,851 miles exactly being 25 % ... and the 15,404 miles being FRA-NYC incl. biz bonus.(3851 x 2 + 100 %).