Trending will show that all manufacturers will update their product line to keep up with client demands, advances in technology, and their roadmaps within a product cycle and or life.
The Z3100 is the same as all others. Epson already (as usual) announced their new printers the 7900, 9900 which follow the 11880 on down, all great printers. Canon upgraded their line up to the x100 series which had many improvements especially in inks since the release of the Z.
So an educated guess would be an update in the near future. IF it is at Photokina it would not be too soon.
Pricing normally stays about the same , only the older models largely discounted.
The current Z3100 is a very capable printer that has some drawbacks that may or may not affect your needs. Are the your needs going to be better met with a newer series based on more or less the old feature set? If so the price will be higher for the updated models, which will taper off as all the printers do over time until the next inevitable replacement cycles occur. These days it seems around two years, but there are some surprise printers too, such as when the 3800 came out.
This Photokina is bound to be a very interesting one , with lots of stuff to amuse us, and amaze us. When the Z3100 came out it amazed us, as it was the launch of the future printers want list.
I'd say wait for 'Kina, it's not far off.