Hmmm... a number of points can be made here.
a) Popular newspaper reporting of scientific issues is only the start of the information trail for those in the pursuit of balanced argument. This story is reported in the 'Mail On Sunday' (for international readers this is regarded as a heavily right-wing newspaper in the UK). The publication has a very conservative outlook (with both a small 'c' and large 'C'); especially with an emphasis on Christian values.
b) The article refers to a forthcoming television program on Channel 4; a UK network whose content is currently under severe criticism following the Big Brother 'racism' fiasco amongst other similarly desperate televisual delights. Let's see how much science and how much speculation is involved with this particular broadcast...
c) Endogenous animal retroviruses have been identified, in addition to other persistent, well-defined, and very real zoonotic animal pathogens such as toxoplasma, which are a definite practical threat. Work on a separate timeline is under way to assess their significance in a transplantation setting. Believe me: the medical scientific community is taking their potential very seriously.
d) If we accept breeding, genetic selection, rearing and killing animals for food, we could ask ourselves what is the moral difference between that and rearing them to use their viable organs? We already accept using viable human organs for transplantation, and in many more cases accept stem cell transplantation from close relatives that form human chimeras. I'm afraid most of these theoretical counter-arguments are already in the mainstream of transplantation medicine.
e) There's nothing very expensive about this animal process that would necessarily restrict it to the wealthy. Talk of "herds" of tissue-compatible animals seems nonsensical.