My guess is that don't leave it too close to the early entry cutoff. If there is gonna be a surge of entries, they are gonna be at that time to take advantage of the cheaper price, so that might push it over 5000. That leaves you only 1.5 months or so.
And yes i do think it will get to 5000. Last year 4200 riders joined in a ride through tiny country towns in Gippsland, where there was little to do except stay on the campsite. On top of that, cycling is gathering heaps of steam these last few years.