Google added the upload feature a couple weeks ago, and that's what has everyone puzzled. Why add a feature just to remove it 11 days later?
This is just a guess, but perhaps the feature wasn't working too well?
I haven't tested this feature myself but I have been reading user reports. A number of people have reported that tyhey cannot upload ebooks. There was a comment left on this blog, and there also several reviews which complained about this option:
Yeah, the download–>upload–>download model is just weird. And it’s slow! I tested a book last night, and it stayed at “Processing” for hours. Okay, I admit, I tested it on a Brandon Sanderson door-stop sized book, but still…
Not able to upload my PDF file to Google Play Books even after disabling QuickOffice. Still not able to discard my PDF reader.
EPUB and PDF'S still won't upload on mobile! Just wish it wasn't so cumbersome to upload them. If I download them on my phone I want to add them on my phone and read right away. Still can't upload directly from my device, even though last update says I can it doesn't work.
Upload doesn't work. Would've stopped me from using other apps, you missed out.
I would bet that the upload function is more likely to choke on large files than small files, and since Epubs average significantly smaller than PDF the latter format was probably the source of a greater volume of complaints (or error messages returned from Google's servers). It would not surprise anyone to see PDFs that hit 50MB in size (or more), but a 50MB Epub file is still the exception (textbooks, mainly, and other enhanced ebooks).
You can find the app in Google Play. But I wouldn't download it; there's no need. Instead I suggest that you wait until the next update.