This has existed since the first version, except it needs to be signed with a valid apple cert.

A .pkpass file is a zipped directory that has a json file and some assets. There's no need to have a more limited version, a pass is already very limited.

The issue is spoofing. Major event ticketers are unwilling to publish passes if there's nothing to stop someone else from publishing a pass that is indistinguishable from their's and thus is an avenue for fraud.

The difference with events is that an ics file is not something someone's going to try to sell you or that you'd want to buy. But anyway, all Apple would have to do is stop checking the signing.