The Television Academy, the Emmys' governing body, is instituting a rule change clearly meant to combat the creep of anthology TV series episodes into the TV movie category. Starting in 2019, the Television Academy has set a 75-minute threshold for eligibility in the TV movie category.
In the past three years, Outstanding Television Movie has been won by a trio of TV episodes: the Sherlock special Abominable Bride in 2016, and then by Black Mirror episodes San Junipero and USS Callister in 2017 and 2018. Of these three, only San Junipero would not meet the new length requirement (USS Callister would just squeak by at 76 minutes). But the institution of the length threshold is an obvious move to try to tilt the category back toward actual made-for-TV movies and not TV episodes that seem like movies. So unless the best episode of Black Mirror's upcoming fifth season is supersized, it won't be eligible.
Other Emmys changes include the creation of an Outstanding Music Composition for a Documentary Series or Special category and a tweak to the eligibility period. For the full list of changes, see the Emmys' website.