That's the difference between the "New Thread" and "New Event" that you'll find in the events forum
There's nothing stopping you putting a tag like (proposed) into the subject line, or even adding a poll to your thread to say something like "Who thinks and EF lunch in Altstetten would be a good idea?" Yes, No, Maybe. Remember to make a poll like that public so you can see who voted for what. That's a bit different to the RSVP system when you post an event.
Once you have enough interest, create an actual event, then paste a link to the event from your proposal thread and close it (or ask us to close it)
Hope it works out - there are a lot of people in Altstetten and a regular EF lunch event would be a great idea - maybe more people could start lunch events in their areas?