The general subject of wills upon consideration seems to have given courts and jurists a good deal of trouble, not only in England and America, but also in the continental countries. The Code Napoleon appears in terms actually to prohibit the making of reciprocal or mutual wills in the same instrument.
Drake, Joseph H. "The Public Policy of Contracts to Will Future Acquired Property." Mich. L. Rev. 7 (1909): 318-29.