I like QUAIS system and Medic suggestion especially. Rushing to a downed solider to check his condition would increase experience and reduce cheap kill/instant kill situations which is disappointing in hardcore/ironman mode.
Imo everything should have a purpose each with pros and cons that enhances gameplay and options, such as.
Anything in quick slot can be used cheaper or reduced time units such as: hand guns, grenades, medic packs, c4, scanners (utility), ammo for reloading. The pro and cons figure themselves out while increases game play option and most importantly: increases combat flexibility for new players.
I suggest players can use any side weapon in the Quick slot as if it's equipped. This would help new players alot when they stuff up there TU system and cant fire the main gun, but they can still use the pistol to reduce frustration. Also I believe would complete the combat feel letting players use alot of TU from main gun and use the new left over on side weapon attacks. This would complete the combat feel and increase fluency. This would also increases players ability to customize equipment as long as you factor the pros and cons this system should work just fine.