I still think it unlikely, because again, every single item you have counts against your total. Health potion? That's an active ability. Fiery sword? That's a passive ability. Anything feat-like would count. Etc.
I think you would find extremely quickly that a hard, inviolable cap of 10 and never more would be too low, even for classes specifically designed to be focused and simple.
Consider that League of Legends, which specifically designs every character to have five key abilities (one passive, three basic, one ultimate), also has six item slots plus wards. A game meant to be played over the course of only 20-40 minutes fails to uphold your standard, despite being shockingly consistent about the whole "only five abilities" thing. I just don't think it's feasible.