Hi Metabyter, and welcome to WebmasterWorld. Yes, the world of SEO is changing as we speak. ;)
I've further anonymized your example, because what you'd posted was for an actual product in a format that included vocabulary commonly used to describe it on the web. Though it would be interesting to see if WebmasterWorld has enough ranking power to rank in Google for that description (even though we're not really relevant to the topic), I'd prefer not to chance distorting the serps by posting the actual language here.
I've exemplified what you wrote as...
product description is for example:
'BrandA Greatshot Z123 30x Optical Zoom Digital Camera, Red'
(Note, btw, that "BrandA" in the above is the manufacturer's brand.)
Title tag For the "title tag", also known as the "title element", the description above is a good basic starting point, but I would shorten the product info in the title a bit. More details on why below...
The title is both to describe the offering and to motivate clicks. Query vocabulary that's included in the title or description also gets bolded in the serps, which attracts the eye to your listing. Up until recently, vocabulary in title was also a major ranking factor. This has changed to a degree, and Google has been rewriting some titles on pages it returns to fit the query. See currently active and highly contentious discussion here....
John Mueller: Title tags "not the most critical part of a page" Jan-Feb 2016 https://www.webmasterworld.com/google/4787155.htm [webmasterworld.com]
Mod's note: Let's leave complaints about what Google's doing in that thread ^^^^, and simply discuss options here. I feel that a well-crafted title can still be extremely important, but you're dealing with some apparently conflicting demands. My feeling is that Google has been demonstrating for a while that it doesn't like titles that are keyword-stuffed, and that it also seems to like the store brand included, because it is increasingly valuing the reputation of the dealer.
You can put that brand up front or at the end, or leave it off to see what Google does. Note that Google only displays 55 characters of the title in the serps, but it parses more. It sometimes suffices to have the store brand early in the meta description, and to include it in the title at the end. Amazon, eg, likes its brand up front, because the name attracts buyers, and because Amazon is very conscious about building its brand.
What you're doing in writing the title is juggling how the most likely queries (including your key identifying factors) will interact with your title as well as with onpage content, inbound links, and nav links within your site... and you'll be juggling all that within the available title display space.
The title essentially summarizes the most important points.. In your example, after the manufacturer's name, the product name and model number are probably the most important. We then get into features likely to be searched, the danger is to try to include too many. It's not clear that many searchers would search for "30x optical zoom", even though it might be a selling point. The pixel count of the sensor, eg, is sometimes a stronger selling point.
I should add that increasingly rankings are determined by a page's context in the web, and that going after keywords per se is a big mistake. That's probably beyond the scope of this discussion, except to say that keyword-keyword matches are only part of the picture now, and as time goes on are becoming less important by themselves in the overall algo, at least for highly competitive terms.
Keywords and meta keywords Of the rest for now, it's not clear to me what distinction you're making between keywords and meta keywords. Meta keywords haven't mattered for years, and are so rarely used for ranking that IMO they're not worth discussing.
Meta description The meta description is not a ranking factor, but sections from it displayed in the serps can affect click-through rate. Last I counted, and it's been a while, about 150 characters get displayed. In a strongly mobile-driven environment of smaller screens and shorter titles, the meta description is also the best place for call to action.
PS: I've not addressed your concerns about content duplication. I hope someone else will pick that up.
