I have decades of experience in event organization starting from student summer camps in high school all the way to developer conferences for hundreds and then thousands of people. Especially with open source events, we found that these gatherings are especially good to get on the same page even on contentious questions and could be very effective to involve new contributors, if you provide the appropriate environment. Here is a model that worked in my experience if you plan to involve people in your projects.
1: Push information in one or more sessions
People like to learn about brand new solutions and approaches, or practical information about well proven areas. Some high profile Drupal projects could get into the regular conference keynote, but it is also worth submitting sessions for your topic in hopes they get approved. Sessions are ideal because you can disseminate a lot of information relatively quickly. They are bad for involving new contributors though, unless starting is very trivial. Which, let's be honest is usually not the case, or you would not invest all this work into it.
DrupalCon Portland is coming up in 12 days and the sessions are all settled. DrupalCon Prague is in the fall though and is accepting sessions right now!
Discussion at Drupal Europe 2018
2: Organize a smaller discussion
I usually suggest people doing a session to also organize a smaller group discussion afterwards. At Drupal events these are called Birds of a feather (BoF) events and have a way to be proposed and promoted on a first come first serve basis. These are great, because people attending do not need to commit to being involved in making your thing, they can sit back and listen. While you don't need to commit to create slides or demos. In fact, the best approach here is if you focus the discussion on problems people have in this area, so you can help solve them. Ideally, show how your proposal solves their problems or at least take this input in your task prioritisation.
For example, I hosted "Multilingual theraphy" BoFs at various Drupal events for years, where people came in to vent about issues with Drupal multilingual support. There were usually other people who solved the same problems before, so the BoF usually ended up with people solving other people's problems and vice versa. So we used this opportunity to grow the community, take the list of problems in our prioritisation and to gather future contributors and testers for our solutions. BoFs are the golden opportunity between sessions and contribution events because the attendee commitment and the organizer commitment are both relatively small if you do it right, but the returns are much higher. Potential contributors who may feel like imposters are more likely to attended a BoF than to show up and ask a question 1-1 or especially to randomly show up to contribute.
DrupalCon Portland in 12 days is still accepting BoF proposals until end of Friday, so now is the time to grab the opportunity. DrupalCon Prague will open this submission later.
DrupalCon Seattle 2019 contribution room map
3: Be accessible at contribution events
Once you disseminated your info at your session and started involving folks at your BoF, the final part is rolling up sleeves at a contribution event. DrupalCons and other events are really good at providing an open space for contribution events. You can show up randomly and claim a table or part of a table and put up your name for it on the contribution board. Consider how many things compete for attendeee attention at these events, and you will realize randomly showing up at contribution does not necessarily have the desired effect. How would others know when to find you there to be involved? If they show up before/after you've been there, it would leave them with a sour feeling. So as with BoFs, it is best to think ahead and pin down when you plan to be actively at the contribution event. Then visibly mark your spot in the room with whatever technique is available. If you want to involve new contributors, I think this usually only works in conjuction with the previous two components, as you would have the folks who got to know your vision and direction as well as discussed their concerns and problem areas with you. Showing up randomly at a contribution event requires a certain amount of courage and the previous two steps help build up the familiarity that would help you be successful here and ease any impostor feelings with new contributors.
4: Wrap this all up and use for promotion
Once you planned your three ways of engagement for contributors, make sure to publicise it far and wide, so people can find you in their right way and format. DrupalCon Portland in 12 days has a summary page with key initiatives posting their plans for sessions, contributions, BoFs, who to look for and what are the focus areas people can help. If you plan to work on a topic at DrupalCon Portland and not yet on that page, feel free to reach out to me and I can help.