Adding the epic tag as "wiktionary definition (if available)" is going to be a little complicated and this is more than one card.

Is there any chance that page preview be available for the Wiktionary projects?

No plans that I'm aware of yet but the first thing to do to get towards that would be making the summary endpoint in rest work with wiktionary content in Mobile-Content-Service

We have a Wiktionary definitions endpoint, but that works only for English Wiktionary (examples bar, and). Other language Wiktionaries may use different page structures, which makes them more difficult to parse.

If we really want the summary endpoint for wiktionary to include the parsed definitions then we would have to implement a lot of different parsers or come up with a way to simplify this.

I wouldn't hold the existing Wiktionary definition endpoint up as an example to emulate. IMO the only sane way of moving forward on Wiktionary integration, given the lack of consistency in page structure or content, is to come up with a set of markup reflecting elements we're interested in (definitions, examples, etc.), and then work with Wiktionary communities to incorporate that markup into pages so that clients can reliably query for what they're interested in. There's a task for this: T138709

The main blocker here, I think, is someone deciding that Wiktionary integration is enough of a priority to justify spending the time to lay this groundwork.

Also, there's no concept of a primary definition in any Wiktionary as far as I'm aware, so that would have to be defined in a product spec.

See also: T176242: [EPIC] Representing / extracting wiki-specific application-level semantics

@Mholloway an approximation for the primary definition could be the first gloss/sense of an entry, skipping all obsolete/archaic senses which are sometimes listed first (presumably to illustrate the semantic development). in case of several part of speech headers this is trickier, since there's often no clear ordering

This is not actionable at this point in time by PCS. Do add the tag again once it's been prioritized by the Web team.