Do you mean something like, let’s announce a new version of a product for next year, so that no-one buys the current version of it this year, or let’s promise something new for next year, so that when next year does arrive, everyone can then complain when we are no longer able to deliver it on time due to events totally outside of our control ….that sort of thing?

Just because a new product is announced, doesn't mean others won't get sold. Like buying a TV you would never buy one otherwise as you always know a new one is coming. It's more the fact they announce everything last minute. Don't care if the time scales aren't met... Things happen, is what it is. Would just be nice to know what is going on, build some hype etc. 

Why would any rational company give their competitors a heads up?

Quite a lot of companies do roadmaps actually. Hardly giving competitiors a heads up when most stuff is already patented. Most the big boys give a heads up as CES as well. Sonos usually has sweet fa at these events. Plus as I said builds hype and makes you want to buy the product. If you don't know what is coming until like a few weeks before, chances are most people have already bought something else from a competitor due to advanced reviews etc. 

That’s not a good example, as new TV models tend to come out every year, unlike Sonos where products are known to stay on the market for as long as 7-8 years at times.  Besides, with TVs, the previous year TV model are usually discounted.

And Sonos keeping these things private are not just about customers, but competitors.  Sonos doesn’t want Bose, Amazon, etc knowing what products they will be selling way in advance, giving them a chance to bring their own similar products to the market. 

Yes, I know that other companies will sometimes give advance notice of new products, but this generally when they have need to raise money in presales, don’t expect it to impact current sales, and don’t have a reason to think competitors will produce matching products.

Personally speaking, I tend to upgrade most things electrical, every 5 years or so, (give or take) …and of course that may depend on the device, but if I had reached that stage and was say thinking of upgrading my PlayBar, but then Sonos ‘kindly’ announced they were going to come out with a brand new improved version of the Arc next year - do you honestly think I would buy the Arc this year? Wouldn’t many folk simply wait and perhaps try to stretch things out and buy the new Arc, next year? 

I would definitely choose to wait.

I would also not be too happy if the new Arc then got delayed perhaps for another six months or a year, due to perhaps a parts-supply problem, or some other indirect reason, even if the delay was beyond the control of Sonos.

I just see several valid reasons why many manufacturers (not just Sonos) choose not to announce their development roadmap.

Boats jamming up the Suez canal, for instance! Or a global pandemic affecting dockworkers unloading ships, or shipping companies shipping across country in a timely manner…..

The challenge with pre-announcing stuff also is the simple fact that you’re never sure, particularly where software is concerned, as to when all the “bugs” are going to be worked out, much less all the features implemented. If it was just straight widgets, it might be easier, but Sonos is much more. 

And, upon review of this thread, we haven’t mentioned supply line issues, such as the current chip shortage, which is causing some companies as large as car manufacturers to idle some of their plants as well, merely because they are missing that extra 3% of electronics, and aren’t confident of when they’ll be more readily available.

Or regulation and restrictions on truck drivers limiting the number of trucks available to move freight.  

Google Assistant was announced early.  How'd that one turn out?  

There are cases where a company announced a future product too early, nearly everyone decided to wait for the future product, the company ran out of cash, and folded.

It has not been the SONOS style, but some companies have a three phase product cycle. New models are released with an introductory sale, prices then revert to the regular price, and the cycle ends with a ‘discontinued’ sale. The idea is to generate an early rush of publicity, sales to early adopters, building to the period of ‘regular’ sales, followed by a closeout period to capture customers who never buy anything that is not some sort of ‘deal’. All of this is planned in advance and profit generated by the product is evaluated on the whole life cycle, not each phase along the way. In one case I suspect that there is only one production run of a product. If the product sells through that batch early, there will not be any product available in that category until the next scheduled product is released.