I could suggest a work based on the principles of biomedical ethics in relation to the presumed consent, as it's a topic in which the autonomy, beneficence, non-maleficence and justice (etc) are extremely involved and may cause a lot of concerns to the donor's family as well as to the recipient and healthcare professional.
Noting that France has implemented a hard opt out system for organ donation on January the 1st 2017 and this differs from the approach that Wales took you may find it useful to look at the following publication -
Your desire for an axiology approach would certainly involve ethical questions rather than the medical impact of the presumed consent in increasing the donor pools?