Lazy image loading for user provided content

[mmd-osm]

Diary and other user provided content frequently includes rather large external images, which slows down page loading. We could force lazy loading of these assets by adding a loading="lazy" attribute to img tags, as described here: https://developer.mozilla.org/en-US/docs/Web/Performance/Lazy_loading

The change is rather small, but I'm not sure if this doesn't cause unwanted side effects. Does anyone have any opinion on this topic?

diff --git a/config/initializers/sanitize.rb b/config/initializers/sanitize.rb
index c9d6a5dbac..f8f2b784d9 100644
--- a/config/initializers/sanitize.rb
+++ b/config/initializers/sanitize.rb
@@ -2,6 +2,10 @@ Sanitize::Config::OSM = Sanitize::Config.merge(
   Sanitize::Config::RELAXED,
   :elements => Sanitize::Config::RELAXED[:elements] - %w[div style],
   :remove_contents => %w[script style],
+  :attributes => Sanitize::Config.merge(
+    Sanitize::Config::RELAXED[:attributes],
+    "img" => Sanitize::Config::RELAXED[:attributes]["img"] + ["loading"]
+  ),
   :transformers => lambda do |env|
     style = env[:node]["style"] || ""
 
@@ -24,5 +28,7 @@ Sanitize::Config::OSM = Sanitize::Config.merge(
 
       env[:node]["rel"] = rel.split.select { |r| r == "me" }.append("nofollow", "noopener", "noreferrer").sort.join(" ")
     end
+
+    env[:node]["loading"] = "lazy" if env[:node_name] == "img"
   end
 )

[HolgerJeromin]

On a website from me I added this HTML property to all user added images (inline images in a blog like page).
Invisible images (down a few pages) are not loaded till the user scrolls down. The browser is smart enough to fetch them early enough, so even if the image size is not known initially the reflow is not visible.

To summarize: I am pretty sure this will have no downside but will be good with many scenarios.