Releases are proposals that are realistic, not only technologically but also economically and that make sense in the telecom ecosystem.
For example as you say, one can dream of a 300GHz, 256 antennas phone transmitting data at 3,200 GBits/sec, but actually no phone CPU or hardware would be fast enough to keep up with such a wild beast (they already have difficulties to cope with the current gigabit/sec rates).
In addition the higher frequency you go to escape the spectrum regulation, the greater attenuation there is in the medium, so at 300GHz you can may expect a path of only a few meters.
You should look at the standard body 3GPP, a consortium of standard bodies, it has releases, not generations and releases come every year or so:
http://www.3gpp.org/specifications/releases
Releases are proposals that are realistic, not only technologically but also economically and that make sense in the telecom ecosystem. For example as you say, one can dream of a 300GHz, 256 antennas phone transmitting data at 3,200 GBits/sec, but actually no phone CPU or hardware would be fast enough to keep up with such a wild beast (they already have difficulties to cope with the current gigabit/sec rates).
In addition the higher frequency you go to escape the spectrum regulation, the greater attenuation there is in the medium, so at 300GHz you can may expect a path of only a few meters.