In order to send events having the meta.dt field. Product teams have indicated that these timestamps must be generated client-side, and this is doubly important due to the upcoming buffering of HTTP requests for sending events. Should this be something incorporated into MediaWiki core?
Also something to debate is whether the time recorded in the timestamp should be in UTC (as supported natively in ECMAScript 5), or reflect the local time offset (still being formatted in ISO 8601). The latter is supported in the ISO spec, just not in ECMAScript 5. Both could theoretically be supported, but for the moment I'm interested in what we would want for e.g. client-generated events which need to carry a client-side timestamp as one of their properties.