I doubt that Al Michaels (who isn't a spring chicken anymore mind you) appreciates the added work-load and being at risk of overexposure. Hell, I already don't like the idea of the NFL insisting on having Jim Nantz and Phil Simms (CBS' #1 NFL announcing crew) do Thursday night games either for the same reasons. Also, this essentially, waters down Sunday Night Football, which is the NFL's marquee game of the week.

https://www.yahoo.com/tv/nfl-blocks-mike-tirico-calling-nbc-thursday-night-173858536.html

The NFL (https://www.yahoo.com/sports/m/5344de36-09ac-3a41-9ffb-e1ee65736f96/nfl-issues-statement-on.html) has blocked (http://awfulannouncing.com/2016/report-al-michaels-not-mike-tirico-will-call-thursday-night-football-for-nbc.html) NBC’s proposal to have Mike Tirico call “Thursday Night Football” games, which felt essentially like a foregone conclusion for those who follow sports media. Tirico successfully handled the play-by-play duties for ESPN’s “Monday Night Football” before NBC Sports hired him away. The able and talented Tirico came aboard in time for the Rio Summer Olympics, and the assumption by many was that he’d take the Thursday (https://www.yahoo.com/sports/m/22299e00-49ab-39b0-9e7e-a8ed8c72c85c/al-michaels-will-handle-nbc.html) pigskin while Al Michaels (https://www.yahoo.com/sports/m/22299e00-49ab-39b0-9e7e-a8ed8c72c85c/al-michaels-will-handle-nbc.html) stuck with “Sunday Night Football,” broadcast’s top TV series.