I'm sure the aco would be unwilling to give up any income form camping, however the annexe site is not owned by them if the info I heard is correct, therefore they have little control over the use and proposed expansion of the tecnopark.
Like you I have also booked the annexe and have not been told that it may be built on, but this knowing the past record of the aco and camping passes this should not surprise anyone!
As a back up we have made plans for another site to avoid being dumped in basejour or another new site still more remote, if the info proves correct.
Having said all that, it is nothing more than a rumour at present, and lets face it we have heard it before, which is why I posted it here in the hope of more info.