Hey @leonard84, I'm currently working on this feature request. Would you please clarify why you are intercepting calls to at? Is it to act on page changes (as in "Page change listening") or do you actually need a callback before and after at checking for a page occurs? If it's the latter we could introduce a onAtCheckFailure which would allow users to implement whatever additional reporting they'd like to have on at check failures rendering #584 redundant.
@erdi I would like to use the hooking mechanism requested by @leonard84 as well. Unlike @leonard84, I haven't figured out how to get Interceptor magic working to intercept those methods but as an intermediate step have defined a custom navigator which overrides those methods in the Navigator class. But with my approach, TemplateDerivedPageContent events can't be intercepted.