I agree there's a lot of interesting things to discuss about this topic. It can hardly be contained in a short survey like this.
For the additional thoughts I put: Positive: Selfish human thinking restricts most people to considering only how their actions will impact the world within their lifetime. The potential for living hundreds or thousands of years could allow people to think more long term about their actions. Very few things are persued in the 50-year time span, let alone planning for something that could take 200 years. Negative: People may be much less willing to take risks. If the only things that can kill you are possible to avoid entirely, wouldn't you?
I hadn't considered how bad the unequal access could be in the way that you talked about. I was thinking it would be one of those things like advanced cancer treatments, for example, that the mega-rich get access to when it is first developed and then within a few years to decades it becomes the standard of care. What I didn't consider is that whatever the breakthrough is that allows immortality may need to be near-constantly applied for it to work. Almost like a potion of immortality that lasts only weeks. Even if the cost of the treatment is lowered very quickly it's not likely it will be something as simple as insulin for treating diabetes or aspirin for treating blood pressure. It could take decades for it to become affordable for the upper class and may never become economical to give to everyone. Having a class of people who die of old age and a class who doesn't is some super dystopian cyberpunk type shit.