You bring up many valid points, so let me put on my frontend dev hat and make some more work-related observations.
First, I think the BBS is doing everything right. I have a lot of respect for the work @codinghorror has put into the development. I also think Imgur is making the right decision to deliver smaller formats instead of the bigger GIFs, since those with older browsers are also those with slower connections. And this is important to note.
I myself develop according to the 1% rule, that we should only provide support for browsers that have at least 1% market share or visitor share according to the logs. But how to deal with those that are no longer supported? If I take the LinkedIn route, I am alienating those with screen readers, or those still using their older Samsung phones that are no longer receiving updates. So I allow for graceful degradation, that sure, the latest and greatest can be used, but when things break they only break little bits but not the entire site. This seems to fit my clientele, as our customers are farmers and construction companies, who have other priorities than to keep upgrading their computers.
What this old Safari does is when a Giphy image is WebP, it shows how big the image would have been and the alt text. It lets me get a feel for how important alt text is. Lets this happy mutant see how it feels to be behind the tech curve. And most importantly, it shows me why graceful degradation is still important. It makes it easier for me to imagine what it would be like for vision impaired people who have the screen read to them.
So yeah, in praise of older browsers. They keep us honest.
