In all honesty I quit caring about terraria with all the delays and bugs anyways. If this update never gets released it will be no skin off my

. Personally I don't set estimates on my completion time unless I know for fact that I will hit the mark with a product I would be proud to put my name on. The key to success is to overestimate the time a bit to allow for leigh way. Either you finish on time or early and who isn't happy if you finish early.
Going based on your current track record I would say this update won't be ready till mid to late q1 of next year. Simply because there would be absolutely no point in trying to compete with the influx of triple a titles around this time of year. With an already outdated game and most players having moved onto something else I feel it would be difficult for them to justify a q4 launch when most people will be looking for a new game rather than an update with 2 year old content.
Using this logic I forsee a q1 2018 release.