I was offered one of these back around the late 90's when stocks had been booming from, I think, by Merrill Lynch. IIRC the it was tied to both our house and stocks. The paperwork was not clear about one thing so I called them to ask them.
I wondered, What happens if the stock market crashes and our stocks go down a lot?
I was told "We issue a margin call and you just have to pledge more securities. Or we will sell them."
"Uh, what about the house?"
"Oh, if necessary we will sell that, too."

I also asked, since both the house and the stocks are pledged, what if we sell the house? "We call the loan. You'll have 24 hours to come up with the money or we sell the stocks."

Needless to say I dropped that idea. Not good to risk your house. Not good to be locked into that specific house. And sure as shit, if they cease it and sell it they will sell it for a low price to get a quick sale.