Shipment is a tiny map, made for a game without killstreaks, or at least a game that didn't have MW2's focus on killstreaks.  You spawn, throw some explosives, die, and hope your Martyrdom takes out the guy that shot you.  It was quite fun, being a different experience than the rest of the game's maps.

It was also fun that if you enabled "Oldschool" mode, you could get on top of the shipping crates.  (I miss Oldschool mode.  It made the game more like an older FPS, with weapon pick-ups on the maps, powerups, and an increased jump height.)

I hate to think what a Support Osprey would do on Shipment.

Rust is MW2's "small" map.  It was larger than Shipment, with a more complicated center while simultaneously being more open (since you could get higher viewpoints, where Shipment was flat ground.)  Some people loved it, others hated it.

Like Shipment, the Support Osprey or Support Stealth Bomber could be ugly.  Assault air support could get ugly on Rust in MW2, and MW3's Support means you don't even need to stay alive to call them in.

I use Rust as an example of how MW3's spawns are poorly designed, because despite its size and openess, it didn't have the degree of wtf spawns that you see in even larger MW3 maps.  If Rust and Shipment are released for MW3, it could be interesting to see the results.  Will IW change the spawn points?  And if they leave the locations alone, will the maps still see the MW3-style bad spawn moments, or will it be closer to MW2?  (The results could give more details of just where MW3's spawn system goes wrong.)

One other issue is that MW3 already has a lot of "around the corner" death moments on existing maps, which takes away some of the point of Rust and Shipment's fast death gameplay.