Regarding V'Ger, I have heard an interesting theory that the singularity that Voyager 6 passed through deposited it not just in a different part of the universe, but back in time, possibly thousands or millions of years. This would account for how V'Ger was able to explore the entire universe in so short a span of time since leaving Earth.
As for the idea that the machine planet in TMP was the Borg homeworld......I don't think it was the Borg that discovered Voyager 6, but there is an intriguing line in the Nero
comic mini-series, where Nero, having encountered V'Ger, remarks that it and the Borg are both the offspring of this machine civilization (This is what draws the Narada to V'Ger, as the ship includes Borg technology, and thus regards V'Ger as a kind of "cousin"). I figure some renegade machine intelligences left the planet at some point in the distant past (whether it was before or after Voyager's rebirth as V'Ger, I can't say now) and journeyed to the Delta Quadrant, where they bonded themselves to organic lifeforms, thus eventually giving rise to the Borg.