Hardcore doesn't have a different number of mobs as far as I'm aware. I believe all difficulties (including peaceful) have the same number of mobs spawning, they just do more damage and have more health in harder modes.
True, have you seen how big the creeper holes are in hardcore?!?!?
No. Easy, Normal and Hard are enough. If you want a more challenging experience, set yourself a goal in hardcore mode, like not using swords, or killing every monster you see.
Also, I doubt monsters to come are going to be restricted to higher difficulties. They will be added to all difficulties, just nerfed where necessary.
there should be very much creepers, zombies, spiders, skeletons and even endermans.
True, have you seen how big the creeper holes are in hardcore?!?!?
I am talking about more monsters to come not the effect they do
Also, I doubt monsters to come are going to be restricted to higher difficulties. They will be added to all difficulties, just nerfed where necessary.