As mentioned on the mailing list last month ( https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2016-May/012743.html ), there are notes and a transcript available from a few conversations between some Bitcoin Core developers.

Transcript/notes: https://bitcoincore.org/logs/2016-05-zurich-meeting-notes.html

Summary: https://bitcoincore.org/en/meetings/2016/05/20/

This transcript covers topics such as:

* segregated witness (segwit)
* error correcting codes for future address types
* encryption for the p2p network protocol
* compact block relay
* Schnorr signatures
* signature aggregation
* networking library
* encrypted transactions / committed transactions
* UTXO commitments
* merkleized abstract syntax trees (MASTs)
* mutation testing
* key derivation scheme proposal for Lightning Network
* child-pays-for-parent (CPFP)