Without the ExpressCard/34 eSATA, higher speed external hard drive options are not available to 13" and 15" new MacBookPro owners.

WHY did Apple omit ExpressCard/34 from these?

It would have been great to have the benefit of a small but powerful 13" MacBookPro while on the move, away from office/home. And at home be able to plug in a high speed eSATA RAID array to a eSATAcard in the ExpressCard/34 expansion input and connect the laptop to an external 1080p TV/monitor to do full true HD video editing.

Is such a thing possible at the (relatively) lower speed Firewire800?

See also my final comment in thread:
https://forum.videohelp.com/topic329740.html#1822247

...which says that 1080p editing with ProRes422 could be possible on a MacBookPro with sufficiently fast hard drive transfer speeds. Not sure if this is still the case with the new MacBookPros that don't have ExpressCard/34 for eSATA.