It is an open question about whether or not SponsoredLinks should be considered WellFormedEntrys in and of themselves or whether they are a form of Related extension. The argument from the advertising folks is that they should be considered a type of WellFormedEntry because that makes it more likely that the ad is more likely to be viewed by the intended audience. If it's defined as an ExtensionModule, then the ad could be ignored by filtering that extension model out of the primary WellFormedEntry data model; in which case the ad ceases to have value.
[SamRuby, RefactorOk] I personally think the google approach of sponsored links (i.e., things related to the query, and clearly identified as ads) has merit. Another example of ads I like is Amazon's suggestions of other books based on the one that you are purchasing.
[JamesSnell RefactorOk] Agreed. The trick, however, is getting content providers to buy off on the method. If uses can filter out the ads programmatically, then they ads have little value. In the Google model, the ads are not part of the core content. They can be filtered out very easily. The bottom line here is simple: separating ads from content is a GoodThing. We need to be able to articulate exactly why it is a GoodThing and why it is preferable over mixing ads in with the content.
[LachlanCannon RefactorOk] I think it has to be sold as a matter of trust. If advertising isn't clearly marked, then people are less likely to trust the feed, more likely to unsubscribe, et cetera. Maybe as part of the specification it could mandate that a particular feed or part thereof is not to be viewed without the ad, if the feed specifies so? It still wouldn't stop it being parsed out, but anyone making a (formatname) reader would not be able to advertise the reader as a valid reader if they fail that guideline?
[GrantCarpenter RefactorOk] Advertisers ultimately drive where their content will end up with their wallets. Once some well-intented developer adds an ignore WellFormedAdEnty feature into his consuming agent, Advertisers will most likely abandon their defined sandbox and head for normal WellFormedEntry-land for good. People will filter/block ads at the client end if possible, advertisers will break from decorum if it means getting eyeballs on their ads. Publishers control the feeds, sure enough--but not all publishers will value standards over revenue. Which is all to say, separate is clean to me, but probably not realistic.