To stay or leave PhD after having completed 4 years
Firstly, no apology needed, your question is thorough and easy to read and understand.  It sounds like you are in quite an unpleasant situation.

Don't take any advice I may give as gospel, but in answer to your questions:

You are most certainly not foolish to wait until now to stand up to your advisor, you have had several leads and have given many chances for the project to kick into gear. You have every right and reason to feel skeptical about the current promises and project direction.

Ultimately, how you proceed is up to you (you're probably understandably sick of hearing that), but look at the following considerations (no doubt many other members will add to this):


The new direction could well be a winner, leading to papers, conferences and most of all, fulfillment.  It could also be a good one as now, you have made your feelings clear to your supervisor.
Could this be just another academic 'false positive'?


Perhaps outline a couple of potential papers and present them to your advisor (this is something I do).  This could be an ongoing thing, alongside your research - outline potential papers.

As for the timeframe, 17 months - I would not be too worried about that - I have been able to get three papers published in less than ten months, with a 4th on the way and the 5th planned (I finish my Ph.D. at the end of the year).

I hope this helps, and I hope it all gets sorted out for you.