I think thats a great idea, but if you get a phazon gun, instead of it changing itself, why dont you just get....;
Orange phazon - You get this after you kill omega metroid X in his final form (overloaded with orange phazon). Kill him and get orange phazon cannon. Orange phazon cannon can burn most enemies, like orange phazon in the final place in metroid prime 1. To get ammo kill metroid X or go into Orange phazon. After getting this upgrade you no longer take damage from orange phazon.
Blue phazon - You get this after you kill the yachtaro-7 from planet salsa 7, home of the mexican people. This phazon is so icy cold the mexicans created it to stop the salsa from burning thier tongues. This freezes enemies and after they are frozen they can be melted with orange phazon. After getting this upgrade you no longer get harmed by blue phazon or ice/cold places.
Purple Phazon - You get this in storage room 4567854567865-940955097262.172674182984 - it adds a specail tank onto your beam cannon than takes in orange a blue phazon, mixes them and adds pure phazon extracted from Tallon XVI (or whatever) and fires to make a phazon that obliterates enemies within 5 seconds after parilazation that followes the blast. This phazon kills enemies by creating extreme heat and cold spikes in thier body temperature that thier body cannot keep up with, makes it slowly decay and melt at the rate of 100 years per second.
Melee upgrade - After killing the sword gaurdian in mutilating lab 2, you get the melee upgrade. This allows you so that when your in your beam-cannon mode, you can hold L-R-A-Y to activate the beam sword. Once in beam sword mode you can hack enemies in close range with A. You have to activate it in beam cannon mode, but you can change it to phazon mode(s) by simply using C stick. The sword carries on the properties of the phazon. After another upgrade, the slash from the sword goes farther and the slash makes phazon-slashes coem from it. A final upgrade allowes samus to use the raw energy from missles to fuel her arm to go into a rapid spasm which allows for many slashes in a short period oh time. Melee mode requires ammo.
Super Mode - Super mode takes 100 of each ammo but is well worth it. You get this upgrade after defeating Dark Samus Omega-Fuzed, which is dark samus infused with remaining power she stole from dark aether. To use super-mode press and hold R and press Y-B-A. Samus than goes into a frenzy which allows her to move faster, take no ammo to fire or make a sword. Makes her take only 50% damage but deal 300% damage, and she doesnt lose ammo. In morph-ball mode the same rules apply, but samus is in a weak death-ball form, she can hurt enemies by touching them.
Phazon Mode - Phazon mode is only an affect and after-affect. Go into raw white phazon pools and hold A to charge samus's phazon tanks to +maximum. She can fire rapid streams of phazon of any colour and it takes no ammo. Enemies drop the white phazon pools and samus can still use this 10 seconds after the white phazon has gone away.
I have taken the liberty of adding my own upgrade =D.
Omega Cannon - This cannon is activated when in pure white phazon. To activate it go into GLOWING white phazon (rarely dropped by enemies) and press C-stick down. This activates the omega cannon which can only be changed after all ammo is depleted. It launches a wall of clear phazon that grabs all in its wake and drags them into the nearest wall, pressing them into it and making them one with the wall. After doing this hold A to suck the enemies in (they SHOULD be changing colour rapidly) and use it to give you 15 of each ammo, 5 missles, and 50 health. Omega cannon comes with 3 charges per blob. You can renew it WHILE in omega cannon by killing 5 or more medium to large sized enemies with one blast and sucking them up. This renews 3 more charges.
I think that would be really cool to have those upgrades. Would someone like to make the suits? Please, only make 3 as there are in all metroid games. A base, an upgrade, and a final (that you get by killing a boss =P) I hope they do come up with a Metroid-3: Corruption (or something) and that its this cool!
as my avatar states- OLIMAR U DUMB@§§!!! YOU LOST LOUIE!? YOUR FIRED- wait, you have an Action Replay? YOU CAN GET MAX CASH!? screw louie and buy me a porta potty!