Hi Elizabeth,
It's brilliant that you've managed to get that many of your members into Slack already. It's not easy getting a 75% success rate on sending invitations out.
It's also really interesting to see your thoughts on what an ideal system would include. I see the challenge of getting people to use any new online system as very similar to that of getting people to use our coworking spaces in the first place. It can be quite a slow process. It took about a year for Slack to become the primary means of communication at The Skiff. And it still doesn't suite everyone.
GroupBuzz continues to be the best service we've ever used for threaded email based discussions:
http://groupbuzz.io I can't imagine Slack ever getting to the stage where we don't need GroupBuzz too. GroupBuzz has created a brilliant on boarding process that anyone who is familiar with email can understand. It's much less of a leap for our less technically savvy members than Slack is. I also feel much more comfortable with all our community's most important discussions taking place there. Since GroupBuzz is bootstrapped (no evil venture capital funding) and owned by Alex Hillman we can trust that our data and our users are safe.
It would be fantastic for us as community founders to be able to communicate with all of our members via a single system with a single message. But I don't believe that's ever going to be possible. Our communities aren't drawn together by a common interest in a single way to communicate online. It feels like a bit too much to ask to expect them to all change all of their communication preferences to match each other. When we want to reach as many of our members as possible we send email broadcasts using tools like MailChimp, alongside announcements in Slack and GroupBuzz. Sometimes we'll even use posters in the space, SMS and/or a telephone call to make sure.
Here's a process I'd recommend for getting members into a new online system (I'm probably stealing some of this from GroupBuzz's onboarding process):
1) Identify 10 people who are super keen. Maybe they already use the system with another community.
2) Invite each of them into the new online system.
3) Ask them (one at a time) something specific that they could each do to introduce themselves or start a conversation.
4) Once some habits have formed with the first 10 using it regularly you'll probably have more people asking about joining it.
5) Brief the founding members to be particularly helpful to new joiners.
6) Invite the next 10 people in and give it a week or two for everyone adjust to the growing community.
7) Continue the process until you've added all your members.
Taking this approach means that most people joining will immediately see some activity that they can get involved with. But it should also make sure that you don't have a sudden spike in an off putting amount of activity that then fizzles out.
Once you have an active community in Slack it makes so many aspects of running a coworking space easier. Having a way to instantly message members turns out to be far more effective than email for many little things that can add up to be annoying.
Slack's integrations make it particularly useful. We're using one (that we made ourselves) to start solving the member directory problem you described:
http://theskiff.coworker.directory/ It stays up to date with the profiles members maintain in Slack.
Hope this helps,
Jon