IIRC, they also discuss the heat of earth re-entry from such a high speed descent is greater than any current heat shield protection would allow.
I just don't see a "billion dollars" being enough to pay for such a mssion, much less how one would solicit the funding for said mission. That's a lot of "10 dollar" donations, and something wayyyy out of the "Kickstarter.com" experience.
Perhaps "scam" was too strong a word, but I can see a lot of money being spent on prep work/studies to somebody
before they decide... "gee, it IS too expensive for us to do."