I'd only put money on one of those options. 15".
Well, I know that Apple always includes mid-range GPUs, so I'm pretty sure we'll see something along the lines of the GTX 1050 or the RX 460M, although I wish they'd go with something beefier. Also, Apple usually puts great CPUs in the Pro line, so I'm not worried about that.
Regarding the rest (16GB RAM and 1TB SSD), the current rMBPs already have that. No chance they'd reduce RAM or storage and I'm pretty confident we'll even get the possibility to order the MBP with 32GB of RAM.
I'm pretty sure the only thing that has a chance of being a disappointment is the GPU. Whether that'll be enough to push me over to the PC side is still up in the air (I really need a pretty good GPU).