Well, as pointed out, the instinctive reaction replaces OA's for the Druid's summoned creatures, and I think for flavor reasons, instinctive actions will be unique to creatures summoned by Primal powers, which appear to be primarily natural creatures.
I *like* the fact that there are going to be several classes with summoning powers, but they'll still have just a tad of mechanical distinction.
Well, I like classes to have dominant traits but not a huge fan of many exclusive traits. Oh well, it goes into the DM tool kit anyway...