Honestly, how they handle the SE and what they add. Right now they have enough characters for me to play endlessly. Now if there are enough modes and a few new bosses to see if it's perfect.
The SE has already exceeded my expectations, and it has provided more substantive additions than DmCDE.
Whereas DmCDE refined and fixed a lot of problems, as well as added more extraneous modes and options for customizing and longevity, DMC4SE has established a stronger foundation and base with three new characters. I do hope that Capcom implements a lot of the new modes found in the DE. If Capcom doesn't, the modding community will.