A couple of thoughts: There's usually no reason to SELL to a spouse, since in the U.S., assuming you have a taxable estate in the first place (currently, an estate greater than $4,000,000), you may make unlimited untaxable gifts to a spouse.
Sales are problematic, since a sale between spouses would still cause any gain in the property to be realized and the owner would pay income taxes on the gain, at ordinary, not capital gain rates.
And in either event, at the death of the first spouse, all the property can be passed to the survivor completely free of estate tax. That is, no tax until the death of the second spouse to die.
Therefore, neither sale to a spouse or gift to a spouse outright, is of any use. It's still "in the estate" of both of them, subject to estate tax.
Now, sale to a spouse's trust (irrevocable) . . . . that's a different story. There must be some "technical detail" left out of the article . . . .
Now, I keep waiting for the mulitmonogamy plan, whereby spouses keep remarrying someone younger than themselves, just to keep the chain going, but since this hypothetical was just thought up by me, perhaps someone could tell me at what point the IRS would kibosh this . . . .