Should we discuss Hard Ciders? There is some similarity to beer in the brewing, distributing and vending of ciders. Or are they "too" different?
If hard cider were sold alongside the wines in the store, rather than in the beer section, would that change anyone's answer? Cider is the result of fermenting the pressed juice of a fruit. Wine is the result of fermenting the pressed juice of a fruit.
The Charmat process that produces sparkling wines in France is also used to produce cider.
They are two different types of drinks, produced in dissimilar ways.
That being said, as wax says, they are marketed to the same audience, kept in the same areas of the store, and are regarded as being of a beer family. I think they could be on topic, we would just have to take care as a group to make sure the answers reflect the spirit (hah! See what I did there?) of the site.
Seems like there are two basic, possibly conflicting, approaches to answer this:
1) Consider the process used to make the product. As noted, cider is closer to wine in production. As such, the questions and discussions of brewing techniques/technology will be less relevant to the those looking for cider information. There could also be less chance that people could usefully contributed to beer discussions if they are primarily interested in cider. It seems like cider would be too off-topic in this case since the motivation is the underlying production.
2) Consider the user base. Cider and beer are, right or wrong, frequently grouped together for sales, at parties, at bars, etc. One reason for this might be the placement of cider on taps. The real issue, however, is that since these two products are seen as very similar by consumers, this site could include cider as on-topic, drawing a greater audience, even if some of the discussion would be technically different from the beer discussions.
I'm not sure I've got a great argument for one against the other. I will admit that I tend to side with 2) since I'm usually of the mind that more people makes a more vibrant community, even if that increases the noise-to-signal ratio.