Traditionally the threshold for capacity to marry had always been viewed as a fairly low bar. Cases such as Southwark London Borough v KA and others (Capacity to Marry)  EWCOP 20 have drawn parallels between the capacity to marry and the capacity to have sex.
However, there has been a few recent Court of Protection cases which suggest that in order to have capacity to marry one has to understand all the consequences of marriage. One of the consequences of marriage, at least in England, is that it revokes previous wills. The case of Re DMM (2017)  EWCOP 33 in the Court of Protection imported this level of understanding into the capacity to marry. That of course requires much more understanding that previously, where the person had a will.
Arguably, if these first instance decisions were upheld, it also imports into the test of capacity an awareness as to what the intestacy position for a wife would be and the impact on other potential beneficiaries.
Clearly the law needs further clarification in this regard. The Official Solicitor’s position is that they oppose any lowering of the bar on capacity to marry. They argue that many capacious people are not aware of the effect of marriage on a will. Why should disabled persons have a disproportionate restriction on Article 8 ECHR rights to family life.