One reason why the mass appeal of the NFL leapfrogged over that of MLB was the more heightened anticipation of seeing a smaller number of games on a more limited timeframe. The NFL has gotten away from that formula by offering more Thursday and Saturday games.
More diverse timeslots will always maintain the NFL's core audience of fanatical fans, but a significant segment of its entire audience is made up of (for lack of a more descriptive phrase) casual fans. Increasing the weekly opportunities could erode that portion of its demographic, but I'm sure that the NFL has extensively researched that possibility--hopefully much moreso than that of NFL Europe.
I'm for the idea unless it impacts the overall appeal of the league. It'll automatically mean fewer Sunday tilts, which is a valid concern. Moving Cowboys/Giants and Steelers/Ravens from the late Sunday afternoon schedule to Thursdays could leave Lions/Rams and Texans/Bengals alone to take up the slack.
That combo could cause a number of viewers to switch channels for other more desirable programming until the Sunday night game. The league could compensate by pushing down more, high-profile, 1:00 pm eastern matchups to 4:15 pm. By doing so, that would thin the intro games somewhat.
All-in-all, it's a good concept, but there will be consequences for sating fanatical NFL fans' thirst for more football during the week. There is also the radically spaced bye week rotation which automatically subtracts teams from the Sunday schedule. Of course, I'm not a proponent of the current bye week system, so if Thursday games either did away with it or converted all bye weeks into one midseason break, I would sign off on it in a millisecond.