If they were to be released today

Nevermind and InCotCK are examples of albums that appeared at the right time and place, filling a void if I may say so.

When MoP was released, Metallica were already pretty known and respected, so actually maybe Kill'em All should be mentioned instead. It was a groundbreaking effort back in 1983.

In short, it would be a complete flop outside of prog circles.

Let's consider two different alternate timelines. In the first, King Crimson had never existed (and thus any bands who now consider King Crimson as a prominent influence would no longer have those influences) but the rest of the music careers of everyone involved in the band continued as normal. In this reality, ITCOTCK was obviously not released back in 1969, and instead the performers and writers from the original album have now decided to record and release it today as the debut album by brand new band King Crimson. By some fluke, although all the members are at least 60 or so, let's suppose that all of the performances and production quality have been captured exactly as we know the album today. 

In this first alternate timeline, the album is a complete flop commercially. It would initially gain quite a bit of interest from prog and classic rock fans for Greg Lake's involvement, although it would be controversial given that the guy from Foreigner is on it, too. Prog fans would end up pleasantly surprised by his performances, pop fans very weirded out. The biggest complaint about the album, though, would be its production quality, which sounds incredibly dated by today's standards. After all, we're talking about the original version here, not any fancy Steven Wilson remixes. In all, it might get around 3.68 on PA for "a decent, largely symphonic release, with a retro feel and an almost excessive use of mellotrons". The lyrics might be considered cheesy and people still wouldn't get "Moonchild". So ultimately, a flop.

The second alternate timeline to consider would be to suppose that all of King Crimson's career had occurred as we know it, and that they achieved the same level of success, but without having released ITCOTCK. Instead, they decide to release it today, with the same assumptions being made about performances and sound quality as we know them begin preserved in this timeline. There would be one big change, though; it would have completely different cover artwork. Barry Godber, painter of the original iconic cover, died in 1970 and would not be able to paint the cover today. Unless Peter Sinfield, a friend of his, had kept it for himself back in the 60's, hung onto it for over 45 years and then convinced the rest of the band to use it as cover art, Court would have a cover more in the style of the other modern KC releases (e.g. Power To Believe, Scarcity of Miracles). Due to its more subtle, less distinct style, the album probably wouldn't garner much attention outside of the current King Crimson fan base.

What would people think of it once they buy it? Again, people would pan it for the poor production quality. This time it would fare even worse, however; it would probably have an average PA score of about 2.74. A sample review: "Here Fripp and co. show that they really have gone senile. A definite nail in the coffin of classic prog and further proof that the older generation of prog "musicians" should have retired long ago. Robert Fripp finds himself joined by more or less the same lineup as he had back when the band first formed back in the day and what they brewed up this time is nothing more than an obvious nostalgia-milking cash grab. Not only does the production sound AWFUL for 2016, but really guys? 45 years later and you decide to name an album after the band, but slightly different? Real original. And worst of all, the album is a complete carbon copy of their brilliant 1970 debut, In The Wake of Poseidon! 21st Century Schizoid Man is a laughably cheesy re-write of Pictures of A City, only with less dynamic range. I Talk To The Wind is a dull, tedious copy of Cadence and Cascade (a particular favourite of mine) but the flute soloing, which is decent, I suppose, goes on for far too long. And don't even get me started on Epitaph..." Ultimately the album would be an even bigger flop if stacked up against the earlier King Crimson releases. And people still wouldn't get "Moonchild". 

Imagining a parallel universe without these 3 albums is an interesting question.

OMG they neither know Nevermind, MoP nor ITCOTKC? How should be their music?

However, the real question is:

Do we ourselves already live in a parallel universe in which milestone albums haven't been released yet? For humans living in a parallel world travelling to visit our Earth, maybe they're wondering the same question, with other references we don't know or can't ever imagine...

KING CRIMSON is the most interesting thing here, by light years.