There are several interlocking issues with the day passes and cross area
participation.
One issue is the fact that the IETF chose a business model in which profits
from the conferences fund the organization and the IETF has no ability to
reconsider or change decisions of that sort. I can see that as being an
existential threat to the IETF in a decade or two since the demand for
(unpaid) external participation is going to grow and the technologies for
supporting external participation will eventually not suck.
Using paid conferences as a profit center is a risky long term prospect at
best. Refusing to adapt the format of the conferences to protect the profit
center worse. And in the case of the IETF the whole purpose of the
organization is to develop the technologies that are undermining the paid
conference model. We are sawing the board we are standing on.
Cross area participation is a good thing but the way the IETF supports this
is terrible. I won't be coming to Berlin because there is only one WG that
I have a reason to attend in person and it is not worth making the flight
for a two hour meeting, much of which is summaries.
I much prefer the OASIS or W3C model for plenary meetings where my WG
session will be doing one or two solid days of design work and the plenary
sessions are on the Wednesday and consist of a series of presentations
designed to inform people about the work going on in each area.
Sitting in watching other WGs is not a good way to find out what is going
on. Area meetings are more useful.