Regarding Soul Reaver, you can find the following in TR7.ELF, the game's executable:
Raziel Autoface Menu...There are also some similar references in BIGFILE.DAT, like "kainscrest" and "status_main_reaver_spectral". Without having a copy of the PlayStation 2 game Legacy of Kain: Soul Reaver 2 for a comparison, it's difficult to know if there is more in common than just these bits. Perhaps Crystal Dynamics was working on a new Legacy of Kain game when they were pulled to work on Tomb Raider, and these are just the remnants of that work? The last Legacy of Kain game was in 2001, so I'd imagine they're not still using the same game engine, at least without having given it a major overhaul.
There are also some Lara-related strings worth noting:
lara_evening_altLooks like Lara will have quite a few changes of clothes. Admit it: you just can't wait to see lara_goth_alt or lara_altc! I do wonder if lara_young is a reappearance of the teenage Lara from Tomb Raider: The Last Revelation.
The other interesting bit is this Amanda character. I haven't been following all the details leaked in previews, but I suppose this might be another playable character, like Kurtis from Angel of Darkness. Perhaps Lara has a nemesis this time around? Or a sidekick?
Also notable, the game is referred to internally as "TR7". The game directory, executable, and supplementary files all use "TR7".
Finally, there is this reference to "meat_turret" in the executable. If I had to guess, this is the internal name for the poor schmucks who pass for enemies in the game. They're certainly not very interesting, at least in the demo, and are hardly more than stationary turrets made of virtual meat.
Nothing surprising here, reasonable to assume it's built on a much-overhauled Reaver engine.
We somehow accidentally left some email addresses as data strings in the SM1 executable, and got a few amusing emails months later.
The Gamecube Viewtiful Joe Red Hot Rumble has data strings related to the PS2 Viewtiful Joe 2 for presumably similar reasons.
Gamecube Worms 3D has data strings from the PC version.