I too have noticed this phenomenon on all news channels. As an American living abroad with an ear for accents, I have become especially aware of changes to the language that have occurred since I left the country. My nieces and nephews who grew up in Ohio all use this pronunciation of -ing as -een.
Watching the news, I have noticed that some people only stretch the 'i' and drop the 'g' in the present continuous form but seem to keep it unaltered when it occurs before a noun as an adjective as in 'demonstrating protesters'. But they do say 'the protesters are demonstrateen'. It seems to be mostly northern white speakers who do this, perhaps because of an unconsciously perceived stigma of saying 'demonstratin' that for them, maybe associated with the Deep South or Afro-American English.
Having said that, I have also noticed that the verb 'to be' seems to be disappearing from the continuous verb forms as well, as in "President Trump tweeting this morning.." This could be a form of headlinese solely restricted to the news, but I can imagine that in 30 years from now we will all be saying‚ "They haveen a beer." instead of "He's having a beer." Oh yes, we will no longer differentiate between 'he' and 'she' either. Language changes!