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.