Quality of Life issues find a place in philosophical discourse at several points. The most obvious of these is bioethics. For example, in deciding upon medical treatment, the resulting quality of life of the patient if the treatment is successful is relevant to assessing the worth of the treatment. This is especially acute in situations of limited resources where it becomes a question of justice who should receive difficult to provide or expensive treatments. Is a person whose quality of life prospects are better than another more 'deserving' of the treatment? For this reason philosophers have written on the issue of whether quality of life measures can achieve the degree of objectivity needed for their role in such decisions.
For my part I see the concept is essentially valuational and thus infused through and through with ethical implications. The nature and importance of the values inherent in any measure of quality of life would be the object of philosophical inquiry.