Keep in mind the culture was far different in 99. The online theme park community was still nascent, and there was no social media so much less "FIRST!" culture and influencers.
That said, and I had just moved to the area and wasn't an AP yet, but I think they did a lot of soft opens. Which is easy, if you think about it, just divert guests headed into Studios with a chance to try something new. Not entirely sure how you do softs at EU, but I imagine something like an invite-only TM/AP preview might work.
Then again Hogsmeade did close to a month of softs, at least, I thought every AP who wanted to see it had at least twice, yet it still had 6-hour lines official opening day. In roughly that same time period, Aquatica opened after only a couple TM previews, and had lines back to the 528 all Summer long, sometimes closing for capacity before its officially announced opening time. So I'm not sure the IoA plan will work this time around.