Exactly.

Either it's Graendal's network or all the references to the trio, or both, or in general the alliance of the two women that will turn out to be relevant.

Jordan has insisted too much on this for letting all go to waste.

Even Graendal's last scene (unless proven otherwise) brought back again the issues of the spy network, the alliance with Aran'gar and her deep interest in the plans of the trio.

And while the alliance is new from KOD, the other two issues have been returning frequently in Graendal's POV and scenes since LOC (she even makes references to Demandred in her first scene).

About the spy network, two things comes to mind readily. Either Jordan brought that up to flesh out Aran'gar's motive to seek an alliance with Graendal, or it is "a gun" to use in the third act. Aran'gar could inherit the network, but it seems a little complicated.. how will she manage to get it from Graendal when Graendal dies some weeks after their alliance? It seems more likely that it's not the gun as such Jordan planned to use, it's the fact it's already been fired, ie Aran'gar might gain important information from Graendal, information she got from her spies.

As for the network itself, a great deal of it will fall apart with Graendal's death, all those compelled people who aren't DF but spy for Graendal (and who speculatively exist, anyway. Sammael pointed out she preferred to use non DF as her agents). Most of her contacts are probably unknown to anyone but her (though if Aran'gar was to profess intentions to go after Mesaana to bring her down, Graendal may see fit to provide her a few agents she could use near her, while keeping a few secret ones she will use to watch both Aran'gar and Mesaana going...). A fact we can surmise easily is that Graendal won't look favorably on the fact Mesaana got a free hand on the WT with Aran'gar gone, especially that Mesaana claimed to Moridin her power in the Tower increased each day, and more and more were coming serve the Shadow, knowingly and not. Graendal knows Mesaana and Demandred are not in good favour with Moridin, that Moridin wanted her to see this, and that the timing is very good to strike at the duo before they closed rank and solidify their position again. But... Graendal is very busy right now... and Aran'gar isn't.

As for the DF tied to Graendal, it seems to make more sense that Moridin will have Moghedien and Cyndane handle them.. In fact it seems he already has, and it's through her DFs Graendal found out Moghedien and Cyndane spent time rallying all the DFs for TG for Moridin.

I think it's more likely Aran'gar will try to regain a foothold with the Tower before revealing to Moridin she's been forced out of the Rebel camp. Moridin doesn't care that the Chosen undermine one another. It's the rule of the game among the Shadow - it's what the DO wants.

The other thing not to forget about is that Mesaana and Demandred surely hated deeply the fact Moridin invited Graendal to see their humiliation, and forced them to talk of their plans in front of her. Graendal's no fool. She must have understood what Moridin did motivates Mesaana and Demandred to find a way to take her down. That too could very well motivate Graendal to find opportunities to finish off Demandred and Mesaana, and she has an ally among the Rebels, and Graendal likes to use other people to face her rivals.

As for the ways in which Aran'gar wanted to use the DF network, I wouldn't be too sure it's all about killing Rand.

Having a very vast network of DF means Graendal very likely has DF contacts in many territories, and so she has contacts with many DF who are serving her rival Forsaken. Aran'gar may mean to use the network to scheme against Moridin, Demandred, Mesaana, Semirhage. Bringing down Moridin is yet another goal she mentionned in that KOD scene. It would also make sense Aran'gar thinks Graendal wouldn't approve of using agents that can be tied to her to bring down other Forsaken. If it backfires, it's Graendal the target will be coming for, not Aran'gar. Combined with this comment about "her games" pretending to be other Forsaken, I'm guessing Aran'gar intended to pretend to be Graendal to give orders to her agents. It could be to kill Rand, but what are the odds simple DF would manage that when so many Forsaken died trying? As I said, she could very well also intend to interfere with the other Chosen's plans, pretending it's Graendal who does. She does also mention her "allies" often found early graves...