I just wouldn't buy it... Regardless of how GT8 turns out there's no way in hell I'm buying in the first month of launch. If it's obviously a complete package 4-6 weeks in, I'll buy but if it's not I'll either wait until it's complete or just never buy it.
Sure, this is the way the industry is now, but they still have to lie and promise things they never have any intention on delivering in order to get the initial sales. If they just came out and said "this half-finished copy/paste of our previous title is it, take it or leave it" it wouldn't do well. They'll obviously never do that, they'll keep lying to get sales, so I will not be buying any PD game going forward until I'm 100% sure it's a complete game. If that means waiting three years and buying it at a deep discount, so be it.
By the looks of things most of us are going to be scrounging to find food and keep our homes warm over the next few years, so the "luxury" of paying a studio to beta test their games is going to be falling way down in the list of priorities for most people. In an economic depression the consumers hold a hell of a lot more power than they do in times of bounty, and the onus will be on these studios to meet the demands of the customers lest they go the way of the dodo.