ed25519 adoption -- challenges If ed25519 is that attractive that it seems to be, can someone explain why adoption has been slow and if there are, if any, challenges with implementing ed25519. 

Nathan Aw
In general, assumptions that have been around for a long time are considered far preferable to new ones. Although a new curve is not strictly a new assumption, these curves do have special structure and so may contain surprises. This is not to say that they do contain surprises, and indeed they are not vulnerable to any KNOWN attacks (but that is only what is known). Also, note that EdDSA may be less side-channel resistant than expected, as shown in Daniel Genkin's talk at RWC 2018.