It's very impractical. Aside from the astounding ping differences between the regions, the playoff matches would have to be played at very inconvenient times. How do you possibly balance a bo3 between an Australian team and a European team? Either one of the teams will have 300+ ping or both will have 150+ ping, which are both unplayable. How do you schedule matches between a European team and an Australian team, one will either have to play extremely late, or extremely early, or both will have to play at inconvenient times. TF2 is already hard enough as it is to schedule around work and real life stuff, so scheduling intercontinental matches would be a nightmare for everyone involved.
Besides, there not being a TF2 LAN at the moment is not because there is nobody stepping up to the plate, it's because it's not possible to host one now due to the pandemic. When the pandemic is over, I'm certain we will see LANs being organised again.