First of all, I'm not sure how I feel about an exclusive set for arena. But this is not the point of this thread.
Arena handles things automatically now (okay duh, you're thinking). But that really changed things. You don't have to worry about players forgetting things, or too many different counters, etc.
Mechanics like suspend or phasing are not problematic anymore. Ascend counts your permanents for you, even Energy counters would be very nice to manage.
As a Cardsmith, do you feel interested in creating cards that benefit from arena's automatization? Let's say, for example, some sort of enchantment climate deck that changes every X turns or something of the sort?
(Sorry for bad English)