Great plugin by-the-way, and thank you so much for all the hard work.
Just a general question, about the likely hood of you finding the time to update compatibility to 3.5 following it's release in few weeks. I know you've mentioned some improvements such as switching to a dropdown list instead of a popup and buttons (which I have mixed feelings about, see below). It would be great to see a few improve an for 3.5 comparability to be assured as it's the later LTS release, not sure I can do much to help other than send encouragement and perhaps a bit of info.
I'm in the process of implementing this plugin for our course builders, as a template toolkit. One of the challenges I have is targeting it at staff without making it something that Students are going to start fiddling with, because it's purpose is unclear.
My initial thought was to customise the atto_snippet > 'chooseinsert' language string to add some guidance and perhaps a link to some more guidnance on how to get the best out of our templates. It's a shame this string doesn't support html, so it could be styled and include a link.
So in short, I really like the popup as it could potentially allow me to include some descriptive text, so that users (especially students) know what it's for. I'm not a fan of the 'spider web' icon, not sure if there's a way to allow this to be customised via the config or a language string perhaps?
So if you do move to a drop-down it might be a limitation in my mind.... perhaps you could give it as an option and also make the atto_snippet > 'chooseinsert' string support html, to keep everyone happy