I'm starting to think the right approach for this would be to offer two Base Kits: a TKL Base Kit targeting around $99, and a Grand Base Kit targeting around $150, without any child kits.
That way, people can simply choose whichever Base Kit best fits their needs, and everyone's happy.
I'm not entirely sure yet how MOQ is handled when a set offers two Base Kits during the group buy, but I assume the starting MOQ would be higher than usual. If that's the case, the set would need strong vendor support.
Anyway, I just wanted to share the idea with you. We'll see how it evolves in the future 
For this configuration, I recommend at least one child kit: 40's Mods. Because some people who don't need Numpad also don't have standard TKL boards. Or are you already planning a "Grand TKL" kit that covers smaller boards?
A dedicated 40% child kit in 2026 for an MTNU set? That's blasphemy, lmao.
Jokes aside, the Grand Base Kit would obviously include between 3 and 6-keys 40s support (most likely 3 to 4), just like we've seen with most recent sets.
Then consider moving the dedicated 40s keys from the Grand Base to the TKL Base. It would reduce the price of the Grand Base and attract 40s users who don't want to pay for a million keycaps they won't use. And how many Numpad users want spacebars smaller than 6u?
On the other hand, those who want to cover both types of boards would have to buy both Base kits. But what percent of buyers is that?
You could make an IC survey to weigh customer preferences.
What you're saying is correct in theory, and I agree. But in practice, it doesn't make much sense.
If I start adding more support to the TKL Base Kit (40s, Alice, HHKB, etc.), the price would increase, and the price gap between the TKL Base Kit and the Grand Base Kit would shrink to the point where it no longer makes sense to have two separate base kits. Having two base kits only makes sense when there's a substantial price difference between them (e.g. ~$99 vs. ~$150).
I'm also not sure why anyone would have to buy both base kits, since the Grand Base Kit is literally just the TKL Base Kit plus additional support for those who need it (numpad, 40s, Alice, HHKB, etc.).