As of March, Python devs didn’t know if 2.7 would be part of the main, supported Ubuntu 18.04 distribution. Software in this category is supported for the life of the distribution, even if upstream devs stop maintaining it. It looks like the python2.7 package for bionic is in main, so theoretically Ubuntu is responsible for continued maintenence until 2023.
Ubuntu is being proactive by shipping only Python 3 by default in 18.04, and I expect this will be the last Ubuntu LTS that officially supports Python 2.7.
I haven’t read up on the Debian or Fedora Python situations, but I would be surprised if there weren’t at least community-supported packages for those distros for the life of Melodic Morenia.
To maybe better answer your question, the migration wiki mentions that ROS2 only supports Python 3.