1) It was not immediately obvious to me that I have to select the name to msg. iMessage deals with this by having a specific messaging icon that makes it clear.
2) I was able to guess that the grayed out names meant no messaging but then again I tried to call multiple of these contacts and it does not seem to work properly in that that I can't seem to reach those people. Not sure if this is broken... Part of this is the legacy of Redphone/Textsecure so as Signal spreads as a single app across platforms, I'm hoping this issue somewhat goes away. [1]
3) It would certainly be nice to have the whole contact list be visible instead of just the known contacts with Signal/Textsecure/Redphone along with the ability to easily share an invite to others to use Signal via iMessage, email etc. (use the standard iOS share dialog) I'm willing to bet this gets a lot more people to see/use/invite others.
4) I would argue that groups/multi-device is the same abstraction in this case (each device would be a hidden subcontact) hence it should be possible to get multi-device support in short order if group support is already there.
I don't believe any of the things I've listed above have security implications but I could always be wrong. Maybe I'll file some tickets this weekend if I have some time.
I did some digging and found the link below. Requiring people to understand and handle an issue around a bloom filter is a bit much. That part should just work.
[1] http://support.whispersystems.org/hc/en-us/articles/21274348...