First off, the time frame for this feature would be a long ways off - engine designer revamp at the earliest, probably post-launch update at the latest. But it’s something that I’d REALLY like to see, now that we have a modular framework in the Unreal engine.
The suggestion is simple: allow changing cylinder counts in the variant selection, just as we can change bore and stroke. This would allow you to produce different cylinder count engines in the same factory, like in real life, and would give a legitimate reason to use 90-degree V6s. Considering how expensive factories are in the campaign, I think that this would be a very useful feature. We will actually be able to have a family of engines with a wide range of displacements.
This wouldn’t have to take up a lot of UI space, you can use the single-column cylinder count selection from the first page and put it next to the variant capacity sliders on the second page.
Edit: For a slightly less lazy answer. IIRC @Killrob said in one of the later LDUs, that using 90 degree V6s if you have been doing loads of V8s would result in better familiarity bonuses than making 60 degree V6s.
To add in my own 2 cents. Perhaps a way to compromise is to allow V8’s and 90 degree V6’s to share a single factory, where then of course you’d have to divide the resources to your needs, so say a factory would normally make 100 V8’s a day, you’d have to divide it to needs, sonpike 45 V8’s to 55 V6’s per day. Bit of course the purpose of this would be saving money on retooling and/or building a new factory (or even allow for a cheap transition, like letting a factory that previously made V8’s make 90 degree V6’s at a lower upfront cost)
But also V6-V8 families, too.