In my opinion it could be an issue, at least if not a Mage2 issue a SEO-related issue.
When we flush the image-cache the images' urls gets regenerated: we all agree on that and that is an expected Mage2 behaviour.
The problem is that images with excellent position in google get removed from the search engine and the new ones will be indexed instead.
There is no guarantee that they will be indexed again with the same position in google. And there in no redirect mechanism as there is with product urls (at least, not that I know of).
We saw thousand of images disappear from google just 2 days after an upgrade (from 2.2.x to 2.3.x). Btw, we don't see errors in search console though (and robots.txt looks just fine).
I'm trying to understand if the issue can be linked to other factors but so far the indexing of a cached version (before the upgrade the image cache was not flushed for months) seems a major SEO drawback.
I reckon that sooner or later I'll end up giving it a try with developing a module that generates xml sitemap with images' url NOT coming from the cached version. Cache crawling must be allowed so google can test mobile issues with the images, but telling the crawler to index catalog images (the ones not in cache) won't hurt if we find a way to avoid (possible) duplicate content.
