I get it. The more time that passes, the less likely and the less viable Shenmue 4 becomes. If people think Shenmue 4 is suddenly going to happen, out of the blue, almost 5 years after the release of Shenmue 3, then they are naive.
I get people's frustrations, because most developers use Kickstarter as a springboard to ensure that they have the means to continue or produce a franchise. Yu Suzuki almost had tunnel vision though and seemingly had absolutely no foresight. He didn't do enough to save Shenmue.
There isn't a whole lot people can do. By all means, don't give up. Continue to voice your support for Shenmue 4, hijack polls and do tweetathons etc. Show there is still a demand. But if Shenmue freaking 3 itself couldn't demonstrate there was a demand, then I am not sure what else would convince the powers that be.
Edit: To be honest, I don't think Yu Suzuki even wants it that much. I don't sense any hunger from him to finish the franchise or to make Shenmue 4. I wouldn't blame him either. I imagine Shenmue 3 took a lot out of him.