You really underestimate the timeline here. This isn't a multi-million dollar endeavor. This is a quality niche game. There isn't the manpower, nor would it scale because the audience simply isn't big enough. TiTS and CoC2 are already on danger of cannibalization. If fenCo would undertake a third project, it would likely be outside of this area.
Its the same issue that non-scam startups have. The first time they land a big contract, they implode. Because:
1. Get big contract and first big money
2. Hire people because the contract is big.
3. Suddenly deal with a lot more costs and overhead, because you suddenly have a lot more people.
4a. Run over project cost, and close down
4b. Finish the project under budget, but implode because you cannot land another big contract immediately after.
4c Somehow, you pull it off.
It's not really underestimating a projected timeline. Any good project manager or design lead will and does accommodate for delays, content creep, revisions. It's a part of any production, even a quality niche indie game like COC2. As for COC2, the idea isn't to take away from TITS. I know well enough about how the staff are shared. But text adventures have been built and developed on shoestring budgets since the 1980s. Text adventures, even of the erotic flair, are not a mythic chalice that comes down from the heavens. It's the grind, bugs, and rolling schedule of submitted and approved content staggered on a flexible timeline.
Besides, that's an estimated timeline. I know very well it's unlikely to be achieved or started.
Also, to be a little more in depth/clearer (lol):
1. Comparing a product as service model to any startup makes no sense. Startups often go through rounds of funding from interested investors, financing groups, and venture capitalist firms to expand with a projected ROI on a somewhat firm timeline with milestones. Patreon content creators/indie companies are not like capital funded startups. Now, if Savin and the team decided to go Kickstarter for the last leg of the game, that's much closer to what you're getting at. Still, it wouldn't make any sense for them.
2. There's a cadre of freelancers and active passion writers available. Given the successes of them, it's a no brainer to bounty out the fundamental concepts, enemies, and story npcs the main writers and leads can't do. No, you likely aren't going to make a waifu/npc romancer/fuckbuddy because that's what the main game is for. Yes, you will be under a firmer grip from a lead writer who has a clear vision and scenes/content that needs to be written and divied up to their junior writers and freelancers. But any freelancer, regardless of writing erotic/smut to ghostwriting a memoir for your local bum who becomes an overnight business guru on Craiglist totally well-paid gig, knows that. You're a contractor/do it for free because you like it/have time/etc.
Now most people don't want to get paid in exposure, but...well, if you're a freelancer who's bored or passionate, that's on you. To expect being paid pro-rated market fiction rates by a talented but limited indie team is a naive. Most pro or semi pro short fiction writers make 300-500 on any 7000-10000+ word short story, aka the equivalent of a few smut or event scenes, at the top ranks of writing markets. Writing, for most people who pursue it, is a passion or hobby. Getting paid is something you should only broach when you've proven and been vetted by any controlling party.
Also, it's what's done by tabletop companies for any adventure path, fluff/splat book, etc. The only difference is you have harder codes/forks that are often modular for a text based adventure. In fact, expanding the team of paid writers even at that point wouldn't make any sense. I mean, Savin's event writer's guide is pretty up front: you create/write the concept. He/the team make the final call.
3. Expansions always have a firm theme, with limited npcs and threads. Given the parser and design flow of the game, you wouldn't have another ten companions, 15+ story npcs. In fact, going more old school COC with limited but story relevant enemies and npcs to the area makes it all the stronger. And having a limited but more hand-sculpted cluster of characters is an easier task.
4. Enemies can always be reskinned from the base game. I mean, that's just smart. The core combat is already designed and number of new enemy npcs can be borrowed from established main game enemies. And with an expansion, it's always theme, theme, theme. I know I sound like a broken record: but it's not a kind of modular where you have random throwaway sexable characters in every map node. With an expansion, you hard limit characters. Do really need two similar enemies/npcs with similar plot hooks and mini-quests? No. You cut one or merge them together.
5. Some companions are more main story relevant than others. That's just the name of the game. Cait, Ryn, Arona, and maybe Brint/Brienne at the moment are the most plot relevant based on the state of the game and older areas. Characters like Quinn, Berywn, Atugia, Azzy are more secondary/tangibly related atm. I'm getting sidetracked, but I want to say is this: some companions will always be more content expansive compared to others. There's nothing wrong with that. To expect every companion to be an intergral part to every scene or event is well...weird?
6. As I said, a tight expansion created some years down the line when most everything is content complete in the eyes of Savin and his team would be nice. Not expected or even considered. But it would be nice. And that's what it comes down to, a lead writer/designer like Tobs or Savin or Wsan or any of the other full time writers. It's a matter of want, state of the game, and fan demand.
I know what I said was long winded but I did want to give a thorough response as to what I actually was suggesting as a stretch goal/idea. Thanks.