Robin Berjon[*puts philosopher hat on*]
It depends on what kind of identity you want :) But, sadly, it's probably not the best option if you want to use it as the authority. Two concerns, one mild, one more annoying (answering both qs):
1. The CID is for a specific immutable version, the TID is for mutable.
Essentially, you can update the tile by posting it to the same TID, so you can have successive versions with the same AT URL, but they'll have different CIDs.
2. Very unfortunately, the manifest had to be changed to work with PDSs. Basically, they retain blobs with #$blob but not #$cid :(.
I considered using the blob structure everywhere but it's *really* ugly. So as a result the CID will change between contexts, even though it's possible to project one into the other.