Since there has been no word of any other mazdaspeed model debuting anytime soon and the death of the MS6 this year the MS3 will most likely be around until the Mazda 3 gets redesigned in another two or three years. However, look for the next mazdaspeed model to be done to the current generation miata.
There will only be 5000 MS3's build for the 2007 model year. But there will most likely be a bigger batch for 2008.