CorkSport has released a new 4” intake. Though they only specify it for the Mazdaspeed3, not the Mazdaspeed6. I have my battery relocated to the trunk, so I have a lot of room in the area where the intake goes. So, I suspect it should work in my 6. But I guess I want to find out for sure.
https://corksport.com/2007-2013-mazdaspeed-3-4-inch-intake-system.html

https://corksport.com/2007-2013-mazdaspeed-3-4-inch-intake-system.html