Guilds will probably be (re-)released in a future ”Journal expansion”, i.e. rules and plastic models at the same time. Given the number of guilds I imagine the minis will come as more generic sculpts with alternative bits (heads, symbols, etc.) that convert them into guilders of different types. So less diversity in body size, equipment, etc.
They have already stated that some of the guilds (but not all of them) are getting PDF rules, from the ones they have Forge world models for and addressed the community converted or proxy models for various hanger ones and dramatic persona. So they won't be in a rush to do a supplement.
They typically focus on the hard copies they can sell in store (i.e the books and in store models) which is the new books and just the Justifiers in plastic. They want people to go to the shop and spend more than they planned. (Capitalism, consumerism etc). The forge world stuff is not a primary selling goal.
If they wanted to do a Guilds/Alliance expansion it would be a massive undertaking. It would be involving at least 4 separate guild plastic boxes more likely all six. Completely annihilating the flavour of the individual guilds is not something that can sell. Just making a generic henchman guts too much flavour and people won't buy them. The Corpse collectors and Water guild are very distinctive looks and can't be used on the same base bodies (the Subnautican is basically an Ogre). And both of them look nothing alike to the Promethium Guild or slavers guild etc.
There is a reason why they don't make a alter Elf and Dwarf kit.
Individual kits for just one guild each with possible options like alternative weapon fits or heads will be a viable project but not across such distinctively difference looks between the guilds.
For the amount of different kits required for a full guild release it would be a release as large as the new edition. Necromunda doesn't do a Blood bowl style format with its Journals and team releases. It is closer to the mainline 40k and AoS in hobby format. New hardback and kits releases.
There is not enough infrastructure to produce a Necromunda only magazine on its own and a Journal release on a much more regular scale.
Back in the old Specialist Games days with Fanatic there was enough spread and interest between the different systems to keep that going but it's a different world now. Battlefleet Gothic is an entirely independent community maintained community without GW input, Epic is in a similar situation. There are whole swaths of the Necromunda community who won't switch to a new edition and maintain themselves.
Blood bowl only survives in journal form on its own because it is a fantasy football (or more properly Rugby) thing.
The internet has done many things. Including killing the physical gaming magazine.
I hypothesise that a Warhammer community download will crop up now and then and the forge world release a few months apart. The alliances still aren't the main gang they are a characterful option.