* Olm isn't a replacement for 'Signal protocol' - it's just an independent (Apache license) implementation of the same 'double ratchet' cryptographic ratchet that Signal protocol uses under the hood for generating message keys.
* Megolm provides the higher layer semantics for using Olm for group conversations in Matrix, and diverges significantly from Signal Protocol as far as I know.
* There's already an experimental FDroid ready build of Vector Android (following the HN discussion on Friday) at https://matrix.org/jenkins/job/VectorAndroidDevelop/lastSucc... - feedback welcome on just how badly the polling-based push mechanism performs on your hardware & network. We're looking at alternative push mechanisms like microG - or just using a more efficient push transport for Matrix to provide notifs.