I don't see a problem with the items: Just don't remove prereqs. As long as you're an initiator of sufficiently high level, you know all maneuvers, and hence meet all the prereqs. However, if you never take a level in an initiator class, you don't know them. An item always contains all the maneuvers of a certain school up to a certain level, but you can't use it unless you meet the prereqs. Now this is also simple:
As with learning maneuvers now, you can also only learn new levels of maneuvers when taking a level in an initiator class - and then only the maneuvers for that class.
So, say, a Fighter2/Warblade 2/ Barb1/X1/Chaosmonk2/Warblade+1 gets all first level maneuvers at level 3, all second level maneuvers at level 4, then stays there for three levels until gaining third level maneuvers at 9, and 4th at 10.
A Warblade 1/Sorc10 only knows all first level maneuvers. If that doesn't contain enough maneuvers to meet prereqs for maneuvers from higher level items, then they don't work. Now a Sorc10/Warblade1 knows all third level maneuvers, hence making it possible to gain most maneuvers via item, later.
The late dip is hence even more useful. However, it's like dropping prices on gadgets: You know it will always get cheaper, but you also want to have it. So you just have to find the right time. The only time this becomes difficult is during high-level-starting campaigns, because there you can build ready to that level. During a progression campaign you'll just have to take your initiator levels when you need them, or when it fits your plan.