I think it's a numbers game and he might be the odd man out. How many back-up DTs do we keep? If it's three then he probably makes it. If it's two, it'll be more difficult. And IMO, he hasn't been that special.
True, but Spencer Johnson was unfairly asked to play OLB in a 3-4. That's a pretty ridiculous request of a 300lb man. He's a natural 4-3 DT, not a "3" technique end in 3-4 like Edwards is. Edwards had the benefit of playing his natural position.