I'd be shocked if Tomb Raider wasn't the big holiday pack-in this year. Given the attributes of previous bundled games, it's far and away the strongest candidate. Looking at previous notable bundles, they tend to be games that stand to benefit the most from being bundled, by which I mean games released during the holiday that aren't guaranteed to perform to expectations if released standalone. Looking at the bundled games last year, Sunset Overdrive was a relatively niche game in the market (~300K standalone first month), and there was no chance AC: Unity was going to meet the sales of Black Flag, given its current-gen only status, and the dark 'parity' cloud surrounding it leading up to launch.
Bundling games like Fallout and Halo would do well from a marketing standpoint, but those games are going to sell regardless of whether they're bundled. Microsoft would do well to take advantage of TR's exclusivity period, and move as many units out as possible.
A Tomb Raider bundle including a 500 GB XBO and digital codes for ROTTR and TR
E for $349 sounds very plausible this coming holiday.