Look through the examples in RFC 8659 section 4.3; I think they're reasonably clear on the scenario you present.
The following RRset requests that only ca1.example.net issue certificates for "wild2.example.com", "*.wild2.example.com", or "*.sub.wild2.example.com".
wild2.example.com CAA 0 issue "ca1.example.net"
No, any publicly-trusted CA that didn't strictly follow the CAA standard would be a Bad Thing and would be considered an Official Incident.
Well, I suppose if you use the same CAs for non-wildcard and wildcard certs, then probably having only "issue" entries is fine. I don't currently use wildcard certs, so I have an
issuewild ";" in my domain name, "just in case". I'm generally in favor of trying to make this kind of thing as clear and explicit as possible. Though, I just looked at a handful of popular domains just now (like, just the first dozen or so names I happened to think of), and most of them had CAA set up but only with "issue" records and no "issuewild" records. so I think ignoring the existence of issuewild when making one's CAA record is fairly common.