I am curious about the future of this field as more and more of our existence can be evidenced using the internet. With figures like Trump using social media to define their public image, it is becoming increasingly more important to document virtual communities and interactions. What elements of our digital footprints are important to you, the historian?
Historians already do! There is an entire field of digital humanities (and more specifically in our field, digital history) which is dedicated to the interpretation and collection of everything digital. This includes both pre-digital sources that have been digitized (whether that is through a .PDF file of a 19th century letter or the creation of a database over the transatlantic slave trade) and born-digital sources. The latter are the source material that you've brought up: Social media posts, memes, YouTube videos, etc. -- anything that was created and published online. I have written a more extensive post here of my experiences as someone who has done plenty of historical research using born-digital sources.