A very common error on openSUSE Tumbleweed is that users keep on running
'zypper up' and then are surprised when things fail.

The only valid way to keep TW up-to-date is 'zypper dup'

I'd like to propose to have an extra warning (should be scary enough for the
user)

In order to not have it 'too TW specific', I'd propose to check if there is 'a
product update' included in the list of updates to do: if so, then 'up' is the
wrong command to use

This info should be available to zypp already, as z "zypper up" contains, for
example:

The following product is going to be upgraded:
  "openSUSE Tumbleweed"


So: there is 'any product' to be upgraded, so 'dup' must be used