I have never played so far as you, so I don’t know the game mode in WT
However, I know the gamemode “Rush” in BattleField, where you basicly do the same, just by planting Explosives at the teams defenses, and fighting on, while the map gets unlocked each time. One team is attacker, the other defender; the attacker team has a certain amount of tickets it has to use to get the next objective. If they run out of tickets, they lose; if they capture a point, they advance, and their tickets are replenished, the defender team has to pull back; if you are as defender in the attackers “zone” of the last objective you held, you are “out of map” and are forced to return to your spawn. You always spawn behind your own objective.
This of course needs maps which are built in a longer way and the defense possibilities usually are: first beacon is 50-50 defendable, the next one is in favor of attackers, and gets steadily in favor of defenders, until the last one is basicly very nicely defendable, but also easily reachable from the attackers’ forces.
Similar gamemodes also are in Insurgency.
It is funny, since it sounds like this, and your idea could actually take parts of this up as well, to make it more complete.
As I read yours, it seems like a “Mini-Rush” with SC objective play (plant bombs, capture beacons) + a war thunder objective type (kill an npc), which SC only operates in PvE, and usually is hard to balance since in SC usually npcs are hard to balance, without making them far too strong or far too easy, depending on a situation. It also all sounds a bit confusing to read; Don’t forget how hard for the population atm. sometimes is just to remember the beacons on the maps;)
Also, WT is much more solo yolo, even in a team, because of the distances between the fights are a bit bigger than usual SC maps.
I would love your rush idea, with simpler mechanics, like battlefield shows.
My own take on “Rush” for SC
Attackers have low respawn time, but a group ticket per stage; Defenders could be forced to play Realistic Mode (one ship each) per stage.
Defenders have to hold the first beacon, until attackers tickets run out.
- If all defenders are eliminated, all defender respawns are reset;
- However, If the attackers manage to wipe out the defenders, they get a small ticket boost.
- if a beacon is captured by attackers, the beacon stays down, defenders spawns move one slot back, all tickets are reset, as are the defenders respawns, waiting defenders get a fast respawn time; a defender still alive will not lose his ship upon death. This is not stackable through stages.
- It could be also two beacons for all stages except the last, like in BF, to force the defenders to split up or keep the middle, like in a one-sided pvp capture the beacons - actually for the first stage all standard (CtB) maps could be used as “start”, with the middle beacon missing for the defenders, and the attackers having no beacons.
- The first death of an attacker if he did not kill or capture an objective costs 5 pts, each subsequent (or previous) death costs however only 1 pt for that player, after a certain amount of deaths, your respawn timer is starting to act like any other match: it gets penalties. The Tickets are for the entire team and are roughly 150% of the defenders fleet strength measured, enough to allow mistakes but still make it an effort. This also makes it an incentive to try to push as defender, and force the attackers to fight a defensive match, with the risk of the attackers sneaking by and taking objectives, and the risk of losing ships needed to contain the fast reinforcement the attackers have.
- If the timer runs out on a stage (8-10 mins), the attackers lose.
- If the attackers lose all tickets, they lose the game.
If they make 3 stages, it ends in a final fight, where defenders have some turrets as defense, while the attackers spawn in a very good position to strike. (Only 1 beacon; Maybe this time you have to carry a bomb there and you get 2 bombs by the dread bomb launcher, which works as dread beacons do with “bombs do 50% damage on beacon”)
A Dreadnaught could be brought in as a prop, where the attackers launch from, and act as a spawn defense of the attackers. The dread moves forward once a stage is taken.
Attacking Players can either spawn at the dread (at last captured location for attackers), or at the usual spawnpoint closer to the objective, mirroring the defenders spawn. At start, there is only one spawn point, because the dread has not yet moved in.
Defenders by default spawn in the standard spawn at the current objective, but can choose to spawn at the back-spawn point, which is the objective of the next stage, except in the end, there is only one spawn point.
This and yours of course needs new maps, or at least a way to unlock an area behind the currently playable area. But I think all these ideas might lead to something, and this can be easily done with the engine as we can see in invasion, there is enough space for this 
Rush is quite addictive, albeit for loot, it should offer both parties loot, if the game had more than one stage of duration (scaled by how many stages your team “won”, meaning a clean defense at the first 50-50 stage gives defenders all the loot, making it an incentive, not to lose a stage on purpose, and prolongue a clean lost match; this sounds often harsh to newbies, but usually, this is part of learning rush gamemodes: the first stage usually wins your game as attackers, if you keep focused until the last stage where the defenders have a slight advantage, but the stage is much shorter, if your team has made its mind up)
At each stage change, there can be a short intermezzo, like “Dread arrives”, “Dread moves to next beacon and shoots the defenses and rocks away with magic disapperator shots to make room for map props and keep the fps sane”; The Defenders final base’ defenses are locked down with forcefields. You can never move over the area of +1/-1 stages, or you get the “leaving the battlefield” warning, meaning if you stay at a place for 2 stages, you will be forced to fall back or get magicly remote detonated.
The Attackers dread is simply a random dread, as it is only used as a prop, which makes spawn camping the attackers in their back spawn “too hard”.