I remember a discussion about, but haven't been able to find it, so pardon me for reposting the argument: at the moment, only full-color PNG & textures are supported, but sometimes this can be an overkill. For a recent project, I've had the need to have texture that were large (to look good on Retina), but basically monochrome, so a grayscale format would have been enough. In fact, running the images through ImageOptim gave significant savings (well over 80%), but the resulting files were rejected by Gideros. Thus, the app shipped with assets that appear pretty large, and it would be nice to get some saving if possible (actually, it's Android users that complain most, with their weird distinction between built-in memory and SD card, iPhone's ones don't seem to care).
In that earlier discussion, PVR format was dismissed by Atilim as low quality (still, that would have probably been enough in my case), but other formats (RGBA4444, if I remember correctly) were seen as a possibility.
However, I don't see anything about in the roadmap: am I missing it, or has it such a low priority?
BTW, as we're at it, aren't Bug #95 & Feature #81 the same?