The trick is that you have passive cooling (a heatsink) in what could be a completely enclosed space (like a glass shade/globe on a flush-mount fixture). The heatsink can't be too big to occupy a similar volume to a 'normal' A19 bulb, or it won't be able to fit in lots of existing fixtures. I suppose we might see some bulbs try active cooling (with a fan on that heatsink), but people are already very aware of hums and buzzes from their fixtures, so it'd have to a quiet one.

I cannot speak knowledgeably to this for A19 type products, but generally there is no need to have such low temperatures to achieve good lifetimes. There may be temperature requirements this low for bulbs mounted in certain locations, but that is not a part of UL 1598 that I have in my brain.

Well, thanks for not answering my question in any capacity, I guess...