Age of Empires 2 Definitive Edition will cost 20 USD (5 USD discount for HD owners) and it will feature a "new spectator mode and tournament features"

Source: https://news.xbox.com/en-us/2019/06/09/e3-2019-age-of-empires-ii-definitive-edition-launching-fall-2019-beta-coming-soon/?fbclid=IwAR3UvAL-F4lwNsPq_exrsEYpa7DdxJcVxVtjSSymx_vgm9v2XlJKvJjnlf4

This post also lists the four new civs: Bulgarians, Cumans, Lithuanians and Tatars

Edit: Release is scheduled for "this August".