I came to terms long ago with the fact that if you want Pokemon games to be hard, you need to set limits yourself. If you want it to be difficult, then do a Nuzlocke or something similar. Pokemon is a game for all ages, and because of that it can never be TOO difficult, or it'll put off the younger players.
I think something people need to remember as well is that you get better at games the older you get. The earlier generations might have been more challenging for you, but you were probably a lot younger when you played them, and weren't as familiar with how Pokemon games worked. I remember Blue as being murderously difficult the first time I played it - I got stuck at Misty, then at Erika, then at Sabrina, and the Elite Four walked all over me until I got my hands on Articuno, which took me an age to catch - but when I revisited the game a few years later, I found it to be very easy indeed; I knew where I was going, what I needed to do to get ahead, and that was that. The game hadn't changed one bit, but I had. Saying Pokemon has been getting easier is looking at things through clouded eyes, in my opinion - are they getting easier, or are you just getting better? I'd say it's a case of the latter more than the former.
I can't see the "Challenge" mode from B2/W2 returning - and if it does, I can't see it being actually challenging - so I guess really if you want it to be hard, make it hard, because Nintendo definitely won't. But I don't see the problem with that - even if you're the kind of player who likes a bit of challenge, it is possible to have fun on an easy game. Just play the game your own way and enjoy yourself~