Naish did have demo glides this year at The Zu - remember picking one up to compare the weight to the Jav.
Trust DJ's advice - you will not be disappointed if the Glide is the type of board you want. And if you get it and don't fully like it or outgrow it, resale will be no problem. But I think the lack of any big and wide Naish boards for resale is testament enough that they're keepers.
Unfortunately Demo fleets are prohibitively expensive and impractical to include everything. My new board I had to take advice from KR SUP centre without trying first. And I am not disappointed because the advice was spot on because they actually know what they're talking about from plenty of experience.
Get the best model you can afford and don't look back.