So a big problem with that is that the long term durability of transparency logs is doubtful. Being a record of every SSL cert ever issued, they're an enormous amount of data, and I won't be surprised if actually getting that data in the future becomes hard.

OTS just depends on the Bitcoin block headers (megabytes/year), and the databases of timestamps maintained by the public calenders, (a few GB/year; it's new entry per calendar per second). It's a more easier to archive a few GB of data than the tens of terabytes in the public CT logs.