How about this kind of URL?
/xwiki/bin/tempresource/Space/Document/plugin/Sjqh73sjq.png
where plugin is the name of the plugin/component that generated the
image, like svg, chart, graphviz...
Sounds good to me for a first version.
I'd suggest instead to use the shorter "tmp" to make the URL smaller
and be aligned with other action names:
/xwiki/bin/tmp/<space>/<page>/<module name>/<resource name>
Is anybody working on this? I'm also in need of this functionality and want
to start working on it.