It is definitely the end of an era. The article mentions that they were late to the game to wireless headphones but they were pretty early, they just didn't keep up with innovation from other companies. It's also pretty jarring that their best selling models are those that have been engineered more than a decade ago. Has 10+ years of experience not taught them anything? Where is the next-gen successor to the 600 series? It seems like the executives have milked their innovation from 10+ years ago dry and are now planning to exit now that ignoring innovation has put them into a hole on the current market.
Over the years it seems like Sennheiser has turned from a engineering-first company to a sales-first company, and ultimate consequence is that the brand name will be the last thing the executives will be able to sell.
Actually there's some good news here guys! It turns out that the articles from places like Verge are using the term "sell" to over-exaggerate the situation as a clickbaitey way to get more hits on their articles; I dunno why I thought sensationaliist online journalism could be trusted, lol.
Here is the actual OFFICIAL STATEMENT from Sennheiser:
Sennheiser's Actual Statement on Their Plans Rather than Some Sensationalist Clickbait Article from Verge
Sennheiser is NOT looking to SELL their Consumer Audio division to an entirely different company. They are looking for a PARTNER/INVESTOR. I learned this from DM-ing one of their sponsors on here who I regularly talk to, and he provided me with that link and this info. It turns out, this is probably a GOOD thing. Sennheiser is looking for an investment-partner for PRECISELY the reasons you are referring to: They want additional funds so they can do a huge amount of research to revamp their consumer audio department and start coming out with some great new stuff! As it turns out, this business decision right here could be precisely what LEADS to the next-gen successor to the 600 series that you've expressed hope we will see! This could be what leads to upgraded versions of the 600, 650, and 660s that have much better sub-bass extension and an actual soundstage, as well as a new 800 that has all the 800's great qualities but without its terrible treble-spike!
Sennheiser has already shown interest in researching and developing such upgrades very recently (as of the last six months or so) by coming out with the HD560s; sure, it has the plastic build of other HD500's series headphones, and it doesn't have AS much detail-resolution as the HD600's series (although its detail is amazing for a $200 headphone). But it has a VERY neutral tuning (other than a slight treble-spike, but it's not nearly as bad as Beyer, AKG, or Grado treble) unlike any of the other HD500's series, and MUCH better bass-extension and soundstage than the HD600's series. And the HD560s has in fact been selling VERY well, so well in fact that it keeps going out of stock on Amazon, from Best Buy, from BH Photo and Video, and even from Sennheiser's own online store!
It looks like Sennheiser is looking to continue to do the kind of R&D that led to the release of the HD560s, but that to do so on a much bigger scale, they need an investment-partner. They aren't outright selling their consumer audio division: This isn't like AKG being outright bought by Samsung, but rather it's Sennheiser looking for a partnership.