Return (Again) to the Golden Wedding Anniversary

Prof. Sidney DeLong of Seattle University School of Law posted this interesting question to the AALS Contracts list. Former Contracts students who recall Hamer v. Sidway, especially those who are now exploring Trusts and Estates, may want to join the fun:

Suppose that at the family celebration William Senior said: "I have made a will leaving $5000 to William on condition that at the time of my death, he has not smoked, drunk alcohol, or played cards for money." Willy forbears from vice but, unbeknownst to him, Senior changes his will to eliminate the bequest to Willy. At the time of Senior's death, does Willy have a claim? I assume that one must impute to Willy the knowledge that wills are revocable. Did uncle make a promise? Does the announcement of a conditional bequest in a will constitute a unilateral contract offer? If not, does Willy's foreseeable reliance on the announcement constitute grounds to enforce the gratuitous offer under [Restatement (2d)Contracts] section 45, 90, or 87? If Willy has a claim on these facts, I think the law of wills will tremble but that is not our concern, or is it?