I think that there should be 4 Tiers like in ETQW. The first two - passive, the last two - active. In this way more class variety will be feasible, exactly the thing that made ETQW so interesting and long-living, even w/o custom support.
IMO, Lazarus greenades should be Tier 3 and be available 1 per spawn. It is not OP at all - 1 such grenade per match is nothing.
So for Medic,
[ul]
[li]Tier 1 - Larger health packs (or they regen faster, depending on health pack system)[/li][li]Tier 2 - Self-defib health boost, once per spawn (is not really passive but still)[/li][li]Tier 3 - Lazarus grenade, once per spawn[/li][li]Tier 4 - Health station deployable, just like for field ops, once per match[/li][/ul]
For Fieldops,
[ul]
[li]Tier 1 - Larger ammo packs[/li][li]Tier 2 - Longer airstrikes[/li][li]Tier 3 - Grenade resupply packs on a special button (like in Shrub mod in RTCW). 1 pack per spawn[/li][li]Tier 4 - Ammo/grenade resupply station deployable, once per match[/li][/ul]
For Covops,
[ul]
[li]Tier 1 - Improved breath control.[/li][li]Tier 2 - 3rd Eye Cam with radar and explosive function (see ETQW), once per spawn with cooldown, instead of heartbeat sensors (not passive but still)[/li][li]Tier 3 - Satchel Charge explosive packs for traps, available 1 per spawn[/li][li]Tier 4 - UAV, with high health, radar and explosion feature, once per spawn + cooldown (like in ETQW)[/li][/ul]
For Engineer,
[ul]
[li]Tier 1 - Increased main weapon range or buffed secondary weapon damage - smth like that[/li][li]Tier 2 - Repair sentry ability or deploy 2 mines (depending on class loadout)[/li][li]Tier 3 - Kevlar armor self-boost, once per spawn[/li][li]Tier 4 - Mobile MG deployable, once per match[/li][/ul]
For Soldier,
[ul]
[li]Tier 1 - Improved speed[/li][li]Tier 2 - Improved Iron Sights with MG[/li][li]Tier 3 - Improved health[/li][li]Tier 4 - Rocket launcher, 1 shot per spawn (just one shot per match is nothing, seems like a joke to me)[/li][/ul]
I am unsure if this whole system will work within 1 map - perhaps too cramped in time even within 3 Tiers. Might be the second half of map will be mainly audible spam from narrator about someone getting dangerous unlocks all the time. I would say it (unlock tree progression) should be implemented not match-wise but campaign-wise (if there will ever be any).