Now that MHW is out, Capcom can start full campaigning for their next big games... or more specifically DMCV.
Start by marketing DMC HD collection. DMC1 on Twitch for free is perfect marketing. DMC games have lots of early potential for twitch views because people will be tuning in to high level style play. Hell DMC3 started the trend of flashy combo videos in single player action games. Get the Twitch people in with a free copy of DMC1 to get them into the series, paving the foundation.
DMC1 over DMC3 as the free game is interesting. DMC3 probably makes the biggest value in the collection so they probably don't want to give that out for free. Based on the rumors, it seems like there might be quite some throwback to DMC1 in DMCV and most people have forgotten DMC1. So making that one free would make the most sense.
Also that trailer is probably indicative of how they will be marketing DMCV. Emphasis the stylish action and 60FPS, hype cutscene and characters. 0 game play of DMC2 in that trailer only two seconds of arguably the best cutscene in DMC2 LOL!