Since I only used GoServ while was worth it, and now all Grimoires are pretty much even, with GoSac slightly pulling ahead in some fights (IMO). So, is up to us to decide which Grimoire we use, so...
What if Grimoire of Service summons a second, or a third, yet permanent Demon? Always thought would be cool walking around with two Felguards, three or more imps, or a pack of Felhunters, just like Kanrethad? I'm talking about a proper scaling here, 1 imp = 3 imps, generating the same amount of fury, 3 Felhunters, one shared cd for their interrupt, and a small nerf in the damage of Felstorm of Felguard.
What do you think about it?