Refactor Unpredictable vs. Extremely Unpredictable, add lessons

[GrumpyOldTroll]

From @michael-scharf (https://mailarchive.ietf.org/arch/msg/mops/eGGPYW2vytPsLwRBlJ38MezPFh0/)

(In Section 3.6. Unpredictable Usage Profiles / Section 3.7. Extremely)

Unpredictable Usage Profiles

I am not fully convinced by the distinction between "unpredictable" and
"extremely unpredictable". To me, these two sections could be merged and maybe
also be shortened. More specifically, Section 3.7 lists a lot of statistics
from the past. What is IMHO a bit missing in Section 3.7 are actual operational
considerations. For instance, are there any lessons learnt for the future? Note
that Section 3.6 has a reasonable conclusion at the end.