@Sissel Cabanela was not planning to, as I personally don't like to use that system. I suspect you'd want to define a new battle phase that runs before it first drops into actor_phase / normal, and probably mess around with the script calls that let you add actors/enemies directly to events.
@Krystek_My I haven't really dug into trying to have corpses that stick around, but the latter is quite possible with only Yanfly's Buffs & States Core. You need a passive state (to manage the psuedo-death status), and then the actual "dead" state.
Lunatic tags on the passive state:
Spoiler
*Drop first, die if hit again*
<Custom React Effect>
if (this.isHpEffect() && value >= b.hp) {
if (b.hp > 0) b.addState(4);
else if (value > 0) b.removeState(4);
}
</Custom React Effect>
*Received healing*
<Custom Respond Effect>
if (b.hp > 0) b.removeState(4);
</Custom Respond Effect>
*Healed via lifesteal, etc.*
<Custom Establish Effect>
if (b.hp > 0) b.removeState(4);
</Custom Establish Effect>
Actual "down" state (NOT the death state):
To summarize: If you take more damage than you have HP, you go into "Critical Condition", where you're at 0 HP and can't do anything, but aren't actually dead. If you take any damage while already at 0 HP, it removes Critical Condition and you die for real. If you manage to recover any HP while at 0, you get back up.
You can mess around with the exact effects to make all kinds of variants- maybe Critical Condition expires on its own after a few turns if they haven't been revived yet, or maybe they can only be healed back up by specific abilities.
Otherwise, you could look into doing some eventing together with the NoTargetSkill plugin I posted earlier and make a summoning skill that only summons defeated allies- it'd probably involve a few other plugins and some clever scripting, but that's how resurrection worked in FFTA2, as an example.
IN OTHER NEWS:
I got a line-of-sight plugin working, though it (predictably) has some performance issues when trying to check whether there's any events in the way. Until I can resolve it, there's a plugin setting to ignore events for LoS calculations.