Ordered Bag Implementation? about artemis-framework HOT 2 OPEN

The Bag is used in Artemis to ensure high performance, but it does not have 
objects ordered by the insertion order.

The EntitySystem has two methods, inserted() and removed(), which you can 
override, and there you can put the entities into an ordered collection like 
ArrayList inside your system. A bit of a duplication, but solves the issue.

I do this here:
http://code.google.com/p/spaceship-warrior/source/browse/src/com/gamadu/spaceshi
pwarrior/systems/SpriteRenderSystem.java

I'm looking into how to add ordered support into Artemis without sacrificing 
performance. Not sure when I'll add it.

Why not order only systems, and only to some level?

From API point of view, for my needs something like

world.setSystem(..., false, order (int with default 0))

would be enough - and then for certain "order" value, the order of calls does 
not matter, but one could place some systems (especially render ones) on higher 
levels. About implementation, I'm wasn't thinking about it yet (Array of 
Bag<EntitySystem> maybe? no idea), but I believe, that:

1) it is enough to solve most cases when we would want ordered processing - 
including original issue (UseShaderProgramSystem updated before any other 
rendering related systems), although it wouldn't solve everything (cases when 
one needs ordered entities, like in SpriteRenderSystem example posted)
2) it does not break compatibility with current code (in old code all would be 
in same "order" at level 0 (default), so it would be same behaviour - at the 
price of maybe single check per world.process to access element of Array (or 
something else) containing Bag with EntitySystems)
3) seems to be potentially faster than fully ordered approach
4) requires least work to solve the issue

what do you think?