@sazberryftw the wordpress.com sites dont need to be manually updated.. its always running the latest version. Its only if your using wordpress on your own hosting.. that you need to manually update it. Infact going to the wp-admin dashboard wont even display the version anywhere.
heres sketchfab working on one of my posts https://chaitanyak.wordpress.com/2016/02/24/what-did-we-leave-behind-on-the-moon/
however i noticed, you have to wait a few moments for the proper preview to show up in the editor.. ie:
In the wordpress.com editor
step 1) paste the link
step 2) wait for the link to turn into the sketchfab model thumbnail
step 3) publish(if you publish before the thumbnail appears, it just posts as a link)
kindof like when we paste a link in facebook
In the wordpress.com wp-admin editor its a little different.
the inline preview does not appear..and you don't need to wait for it.. it works when you publish/preview
to get to the wp-admin ediitor on the wordpress.com site
click on the link at the bottom left of the screen
or go to this link(replace my username with yours)
hope that helped.
the wp-admin dashboard's editor seems to support the Sketchfab iframe embed code!
all you need to do is create a new post, then switch to the "text mode" and paste it here
then when you switch back to "visual" mode, it gives you a placeholder object to do your layout around.