Trump should have just released them all. Could it be possible that some info in there has some relevance/liability to current intel strategy or assets?
The decision hasn't been made yet, it's not something that happens overnight. Whenever something is going to be automatically declassified due to expiration the different departments who own the documents are notified and have 90 days to respond with any requests to keep the classification and the justification used. I've actually posted the relevant laws and regulations on this forum before though it was to demonstrate the ones that Hillary broke and also how it was impossible for the President to illegally disclose classified material.