It's a great idea and initiative to build such a platform/community. I think the platform should have options to do the same challenge but in different time periods (from one day to one year, maybe a day, a week, a month, and a year or other options). The people would be grouped according to the time period they chose for the challenge (they could additionally be grouped by their location and other factors).
Completing shorter periods would give you points and help prepare for the longest challenge period or alternatively you could initially start with the year one if you felt like it. You could repeat short challenge periods as many times as you wish, so for example, whenever you felt like doing a challenge tomorrow, you could "sign up" to a day-challenge group.
But having done this for a month I could say that the most complicated part is perhaps not even the challenges themselves, but the part where you have to come up with something new for each day and find time to execute it amongst your daily schedule. It becomes a job upon itself.
A big part of the complication is that you start doubting which thing would count as something out of your comfort zone and which not, to be sure, the challenge has to be really intense and preferably something you've never done before, it's easy to think about big things that would count (like a parachute jump) that feel truly challenging, but the thing is that big things usually require big resources and plenty of time. To put a truly big challenge into each day is infeasible if you have other things to do.
So you're inevitably left (if not initially then after some time of doing this for sure) with small to medium challenges and have to juggle around with those to find something challenging enough and not too time-consuming. Then additionally even if you find one of those, in practice it might not work out - e.g. you might not manage to get the conversation going with few strangers in a row - will you continue then until you do (could potentially take the whole day) or will you count the challenge as completed because you've tried enough? Completing one challenge will eliminate possibilities for doing similar ones because you won't feel like you're doing something considerably more challenging (e.g. talking to a stranger after embarrassing yourself in public might not seem so challenging anymore and vice versa). All similar complications add up to make the process more difficult as you continue.
The catalog of uncomfortable things to do would therefore be immensely helpful, but for me, it seems the best to do such a sequence of daily challenges when you have free time and can dedicate all of it just for that purpose, it would be like a game or/and a job. People having a gap year and some spare money could take the most of this. Maybe an AI-powered app, similar to this one could help people find the right challenges according to their unique situations/routines/finances, etc. so that the planning part wouldn't get in the way.