Currently the MR mechanism offers only a "Permanent" flag to prevent asynchronous reclamation of resources, but many uses could probably save aside the contents of the resource in a more compact form in another resource space (i.e. reading a hw texture back to heap).  With a callback, existing cases of Permanent resources could instead be "purged" when the resource memory is low and reconstituted later.

This would be especially helpful for Canvas objects that fall into disuse, but still hold onto a permanent allocation of vram.  WebView layers may also benefit from a mechanism like this since most of those are permanent as well with varying levels of "reconstructability".