I can say for certain that VP as a new player is already an intimidating experience. Adding 3/4UC is a lot of new things to learn all at once, and there isn't a good tutorial for it. So there's definitely a downside to integration, along with the up-front developer cost to do it.
That said, I've been somewhat on the fence. I'm not really a new VP player anymore, and I've mostly not downloaded 3/4UC out of habit. We've talked about (and mostly shot down) the notion of a separate 3/4UC mod added to the package of mods downloaded for VP, and for good reason that's not really ideal. But what if we packaged a mod that removed the two new components instead; sort of reverse the problem? Then we can have a new-player disclaimer that gameplay balance is centered around 3/4 UC, but if you want a softer onboarding you can enable the mod that slims down the content.
This also bypasses one of the issues with split 2UC / 3/4UC which was needing to duplicate text changes etc., does that apply in the same way if you're just stripping it out?