I'm pretty sure the Campaign mode will take way longer than just a few hours. The older licence tests were really hardcore, especially trying to get all golds and I doubt GT Sport will make it an easy task to complete everything in only a few hours, as the whole point of it is to make you good at the game because it's designed to be hard.
Also if the game sells well, who's to say they don't have multiple season passes, with lots of tracks and cars being added over time and maybe other modes and features too ?
People seem to be so obsessed with what's not in the game but what if the content that is in the game is still awesome ? Quality over quantity and all that.
Having played the beta, I know the game still plays fantastic, like it always does, so it's certainly not all doom and gloom. I'm actually looking forward to playing this because it's trying something different, not just doing the same old thing again, like every other racing game.
They've already shown some things from the campaign and it is very along the lines of what past GT games' license tests had in mind, so it's easy to guess how the rest of the missions turn out. I loved the license tests in the past games, but only as a starting point, not as the meat of the campaign.
So no, it's actually pretty easy to tell whether you're going to like this game or not already. It's all a matter of personal preference.
Also this whole "whose to say" stuff is silly, and we've already had this discussion before in this very thread even yet again you fall back to it in an attempt to somehow sway people over with potential scenarios of adding in modes if the game sells well and what not. Cars, yes. Tracks, probably. Modes, no idea whatsoever, maybe new online modes sure, but for folks that are interested in more offline stuff, the game selling well could actually make it more likely that those won't be worked on.
This game selling well as it is would indicate to PD that the direction they've chosen to go with this game is the right one, and that direction is less offline content and more online focus. It's actually the opposite, the game not selling as well as they expected could result in them reevaluating what went wrong and the complaints that people had.
TLDR:
-If you think the GT driving model, the cars/tracks featured, the license tests, arcade mode, photo mode/scapes and online racing are enough, get this game.
-If the car & track selection is the main issue you have with this game, then hold off on buying the game and maybe wait. More cars will undoubtedly be added and possibly tracks too but wait it out and see if what they add appeals to you.
-If campaign, the length and structure, in past GT games matters a lot and is what makes a GT game to you, buying this game is not going to help.
-DO NOT buy the game if you're disappointed with the content on display here, and definitely DO NOT BUY based on hypothetical scenarios of what the developer could potentially add in or not when they have made no outright promises or detailed what post-launch content would exactly entail.