First count me among those who have provided "specific, constructive and substantive" feedback. I did so because, like many MANY others, I am part of the community you claim to recognize. Yet your actions and words to this point come across as pro forma, like you actually take us for granted.
1) Many of us do NOT want to give up Slashdot "classic" AT ALL and have said so repeatedly and forcefully. Yet you still tell us that it will only be available until you are done fine tuning the new look. (a new look moreover that we've said we hate)
2) you claim to recognize that what makes Slashdot so special is the community, but I think you fail to recognize a key aspect of this community. We are chemists, physicists, developers, sysadmins, engineers and so on. A HUGE percentage of us are not just geeks, but professionally trained and qualified geeks in some profession that takes brains. Over the years we've self-selected that demographic. Your desire to be "more accessible and shareable by a wider audience." runs the risk of diluting what the Slashdot community is. You are courting a new Eternal September and it appears that you don't even realize you are doing so. boards.4chan.org/b/ would cease to be what it is if it became mainstream. I think you can recognize and agree with that. A flood of pop culture would destroy /. just as a flood of nice average folks would destroy /b/ and drive out the /b/tards.
3) This seriously is a New Coke vs Classic Coke moment. Like the people at Coca-cola, you want to increase your market, I get that. Like Coca-cola, you are attempting to do so by copying the kind of features found among the competition. They failed to allow for the fact that they had spent decades differentiating themselves from Pepsi. Copying the Pepsi taste threw all that away. Slashdot is not primarily a content producer, but a news aggregator, so if you go with the glossy magazine look, what is there to separate you from say Ars Technica? We geeks often make a bit of a fetish out of choosing hobbies, sources of info and social situations that are less accessible to the common herd. In other words, we kind of like being outsiders. If you expand your market, you'd be throwing away that abstract sense of clique-ishness that attracts me to this place. I'm probably not alone in that feeling...
4) At the same time, you're not fixing things that in the group opinion, should have been fixed ages ago. Where is the Unicode and foreign language support? I personally support the long standing choice to not allow full HTML in comments, but I may be in the minority on that. I still think we should be able to incorporate umlauts and other accent characters though.
Here are my straightforward suggestions for expanding your appeal and market without killing off what Slashdot is to us long loyal members:
a) Allow the full Unicode set and such
b) Don't EVER "dumb it down". You can try expanding the range of news items you list, maybe add images to if they are truly relevant to the story, but do not simplify things. In fact; feel free to get MORE detailed, more in-depth. Make your own articles +5 Informative or Insightful!
c) spellcheck, spellcheck spellcheck. There should be more to editing that picking a story and copypasta the summary submitted.
d) You already have slashdot.jp , why not slashdot.ru or maybe slashdot.eu ?(which would feature multiple languages, but probably primarily French and German). While you're at it, put links to the other language sites at the bottom of the page.
e) I for one would love to be able to read the days most actively commented stories from the Japanese Slashdot. (or any other language geeky articles might be published in) I have no idea how hard it would be to implement a *decent* auto-translation of top articles in foreign languages. I think it would be easy to do shitty translation on the fly, so the challenge would be to achieve an acceptable job. I already use a browser plugin and there is also Google translate, but I'm hoping for something that will do this for popular stories. As it is, I have to pretty much guess what stories might interest me and translate those myself using the plugin and the plugin translation is usually lousy