I'm in a different boat than you. I do want the date-based filename to work but it doesn't seem like it is. I updated both my server and app to the latest version. Deleted my old camera upload sync library entirely as well as all the photos, recreated it, adjusted the settings on my iOS app to point to the new library and then initiated a new sync of my camera roll.
I have 3,400 pictures dating back to my first iphone years and years ago. The reason I want the date-based naming is because I now have some photos with the exact same name, 4 years apart, and it causes the sync a wee bit of confusion. I'm about 33% on this new sync and under neath the covers, on my NAS, the uploaded photos are still named IMG_XXXX.jpg. Maybe it only renames it to a date based filename if there is a conflict but other than that, it's still the sourced (sometimes nonsensical) format?
It still feels like this feature is in flux.