Is it just me, or could GW release a Chaos Guard/Lost and the Damned/Renegades and Heretics army while making a minimal number of new sprues? Like, I think they could do a full army release with only 4-5 new sprues.
Vehicles are easy, you just release the existing IG or GSC vehicles with one of the already-existing Chaos vehicle accessory sprues. There's basically half of the kits you need right there.
Similarly, for HQ, you can give them Dark Apostles (probably as a 0-1 choice, since "single Chaos space marine leading a bunch of mortal pawns" is a trope well-established in 40k canon and doesn't require any new models), Chaos Sorcerors (which can use the Age of Sigmar models), Chaos Commissars (new model, 1 sprue) and a Chaos Regimental Command Squad (existing Cadian Command Squad, with a Chaos Guard upgrade sprue akin to the Genstealer Cult upgrade sprues from the GSC releases). Maybe a Chaos Enginseer-equivalent to look after their vehicles; add anonther sprue if so.
Troops are Mutants, Beastmen, Chaos Guardsmen, and Cultists. We already have 40k Tzaangor models, the normal Chaos Guardsmen are just regular Cadian guardsman squads with the same Chaos Guard upgrade sprue, and the mutant squads could just be an ordinary Cadian squad with the old CSM mutation upgrade sprue. The Cultists, though, would be a new 10-man posable kit akin to the GSC models - 2 new sprues.
For elites, you've got Chaos Stormtroopers (Tempestus Scion box with the Chaos upgrade sprue), Chaos Spawn, and maybe squads of weaker Sorcerors (using AoS models, again).
Heavy Support is vehicles and Heavy Weapons Teams, which are just the Cadian teams plus the Chaos Guard upgrade sprue. Fast Attack is vehicles and maybe cavalry, which can just use Chaos Knights from AoS (and it's not like loyalists have current models for their cavalry anymore anyway).
So, an entire army release, for the cost of producing 4-5 new sprues, and tooling new sprues is where most of the cost is.