As a server engineer this sounds like the correct solution. As someone who runs some blogs, not so much.
If I want to put various formats of images on my blogger.com site (or other similar service) today, assuming some syntax was added to HTML to allow it, I can do that immediately. I don't have to wait N years for the people who run blogger.com to update their software.
This is a problem often run into between sys admins who run their own servers and the rest of use who don't. They forgot that the majority of users don't run their own servers.
You can put as many img tags as you want, with any format that you like, today. If your visitors support the formats you're emdedding, then you're good to go. Strategy #2: javascript detection, ala modernizr webp tests.
Most users who don't run their own servers also don't know a thing about image formats - so the point may be moot. :-)
In fact, this is why this problem should be automated. Most blogs are serving uncompressed images, which are resized on the client - worst of all cases.
> You can put as many img tags as you want, with any
format that you like, today. If your visitors support
the formats you're emdedding you're good to go
Hmmm, If I put multiple image tags with various formats that may or may not work on different browsers I'll get lots of broken image boxes on my page. Not quite "good to go" I think. No?
> Most users who don't run their own servers also don't know
a thing about image formats
Really? I suspect that very few web designers know how to run a server but all of them know the differences between .png, .gif, .jpg and now whatever is needed for HD-DPI
The img lowsrc attribute was deprecated a long time ago. If content negotiation isn't going to be used, then a system like that, with separate attributes for the different URLs, makes more sense than overloading the contents of the current src attribute with a custom, differently parsed format (explode on commas or whathaveyou).
The comma delimited list of file extensions was an illustration of a bad solution. The actual proposal was to use proper content negotiation and the Vary header for intermediate caches.
If I want to put various formats of images on my blogger.com site (or other similar service) today, assuming some syntax was added to HTML to allow it, I can do that immediately. I don't have to wait N years for the people who run blogger.com to update their software.
This is a problem often run into between sys admins who run their own servers and the rest of use who don't. They forgot that the majority of users don't run their own servers.