Ok, I created the patch for subtree cycling display inline images.
Tested by edebug when org cycling, it should works fine. I don't know
how to write test for this.

But I got a little problem:

When ~org-fold-core-style~ is ~'overlays~, the ~delete-overlay~ will
cause subtree unfolded. More detailed check out the "org.el" function
~org-remove-inline-images~ in my patch.