I work in the medical field and have considered this often. First off, no one wants to go to long term care, so the question shouldn't be only "how can I afford this?", it should be "how can I avoid it for as long as possible". Secondly, the average length of LT care is not as long as you might think, that goes doubly so if one is realistic about outcomes and chooses to avoid many of the life extending (read extend life at all costs, even if quality of life is sacrificed) medical treatments available. I believe our medical abilities have far exceeded our ethics and morality wrt end of life care.
Considering my first point, I plan to use funds to purchase a multiunit building designed for the elderly. Then, I plan to rent out (at considerable discounts to assisted living) units to other couples who hope to avoid LT care. The synergy of multiple households working together towards the end goal of avoiding LT care will work wonders towards meeting that goal. Cost sharing of any needed in home services, friends living together can rally around each other if one person suffers an injury or illness, etc. Maybe pie in the sky, but I haven't really heard of it being tried, and my highly qualified opinion is that it will be effective. Considering my second point, I think it behooves everyone to seriously consider their personal beliefs about life and it's end, reconcile this with reality, and take whatever legal measures needed (living will, etc) to ensure life is not extended past their personal quantity vs quality measure.