I don't think there will be difficulty levels. But if we do get one, here's what I want (based on Fire Emblem awakening):
Easy: For beginners. No challenge, dumb AI, lenient levelling curve. Virtually no need to battle every trainer to catch up on EXP. Also perfect for speedruns.
Normal: Just like difficulty level of normal Pokemon games.
Hard: For experienced players. Lots of challenge, smarter AI, more unforgiving level curve. Enemies also have more Pokemon. Expect to grind a fair bit. Basically Blaze Black and Volt White without the moveset/type changes, etc.
Hard+: For masochistic players. Unlocked after beating the game on Hard mode. With even more unforgiving level curve. Enemy trainers' Pokemon all possess perfect IVs and often have impossible, cheap ability and move combinations to pray on unsuspecting gamers. Worst part is they're only exclusive to enemy trainers. If you want a taste of soul-crushing unfairness, this is the perfect mode for you.