I don't know what power "schedule" feats
are supposed to have, but they ain't spells.
Some magic items very obviously scale
at the moment of creation ... so it shouldn't
be too hard to make them ~augmentable.
Fighter with Armor of poly/metamorphosis+ is say level 5.
Shield of Plane Shifting is say level 7 with a free action touch send away bbeg thingy.
Sword of Baleful PAO is decent level 9, dangerous to demon lords.
Necrotix Arrows that hit or miss spawn Wraiths or better ... etc
The spells power schedule is well known, why not put magic items there entirely, too?