Of course--that's something I'd expect, considering this new information, and is why King's Rock wasn't an item I asked about. The only effect of King's Rock is adding a chance of flinching the opponent to attacks, after all, unlike Life Orb, which has two: (1.) a primary effect of effectively increasing the Pokemon's Attack and Special Attack by 1.3x (2.) a secondary effect of making the holder take 10% of its Max HP in recoil damage if it manages to inflict damage to the opponent's HP.I don't really think it's necessary to test all these items. It's already been proven that Encourage still allows King's Rock to flinch, so it's not as if it blocks all item side effects.
These will be tested on a "if someone happens to encounter it in battle" basis.
As a result, stuff like King's Rock, Toxic Orb, Flame Orb, Yache Berry, Expert Belt, Flame Plate, etc, which only do one thing, should act normally even on Pokemon with Encourage. It's items that have multiple effects, like Life Orb (and potentially the Choice Items), just like the moves Encourage boosts, that it's curious as to how they might interact, considering this information.
Iron Ball's probably a stretch, but I definitely think it's worth testing how the Choice Items interact with Encourage, considering this information (Encourage stopped only one effect of an item with multiple when it activated, and one that it usually has no effect on (recoil) at that).