Here's an idea that probably only Esperanto has the power to achieve
at the moment, and it could be interesting. Perhaps others may be able
to later on.

Here's what you do: find a blog or site with a certain amount of
popularity but not huge just yet, perhaps one with a pretty good
following and a few hundred to a few thousand visitors a day, and one
that seems amenable to the idea of IALs. This site owner will then be
approached by a large group of Esperantists that have pledged to join
in, and they tell the owner that if he or she writes in Esperanto they
will then visit the site every day, write comments below articles,
etc. Hopefully the group that has pledged to do so will be large
enough that the site owner is given a real motivation to learn the
language - since Esperanto and other IALs can't compete with other
languages in terms of money they will have to do so in terms of
traffic, which is another kind of currency that many seek. We'll say
that the period being pledged is about six months (enough to learn the
language and also long enough that the guaranteed traffic would be
appealing) and the site owner can still write in other languages but
the majority have to be in Esperanto. With a page that gets a few
hundred to a few thousand visitors a day that usually means anywhere
from two or three to maybe a dozen or two comments per day, so with a
large enough group the number of comments will go up too, and it will
be more appealing to write in Esperanto where everyone comments below,
compared to English or what have you where they aren't so frequent.

After the six months is over the pledge period will be finished, but
those that have visited the site over the period of time will likely
keep visiting and the site owner will be good at the language and will
also have a bit of a community set up to respond to so it's very
likely that it will continue.

The number of sites people pledge to visit a day should be quite
small, perhaps only up to five or so. Anything more than that and
there could be burnout from having to visit so many.

Awesome idea.