" Selling that donated stock to Berkshire for 1.15x BV, and thus converting the stock to cash, would cause the foundations to lose considerable value per share that would be transferred to the continuing shareholders including Buffett. Would he view that as a kickback? Tres gauche?"

WHAT? Selling that block to brk would be dilutive to brk BV but accretive to brks IV. No one has any idea if brkb will ever sell below 1.15 xs BV again, after he passes. You know for a fact that selling now at 1.15xs BV, would cause the foundations to lose considerable value ? IF Buffett does nothing, and makes no changes to the 2006 gifting letter, the foundations will be selling 10-15 BILLION a year for ten years. You know what impact that selling will have over the ten year period, after he passes. With all due respect, no you don't and I worry about that selling too. I also think he will fund Melindas new foundation as well, maybe with half of the Gates F pledge. We shall see.