it got to a point that I begin to think whether if you are into all this talent Hunt or contest related activities with the way you professionally operated the entire game,
It's not my job at all, but I must be under some kind of curse because I often end up organizing tournaments, quizz, etc... even when I don't want to

I'd say it was fun

But: it did feel a bit long, especially the part where you wait for the predicted date. And the time to submit a prediction was quite long too, leading to the necessity to edit posts.
Was the rhythm of the rounds (3 days to make a prediction, 2 days of waiting) good ? Too fast ? Too slow ?
Too slow!
What would be the ideal rhythm for the rounds for you ?
A few hours to make a prediction, at random times so people don't get to sleep

I think we are both part of a dying breed, we grew up on the internet with forums. We are used to checking a forum several times a day. Look at the first few rounds, there were plenty of people who forgot to make their predictions.
If we run a contest that requires logging in every day, I’m afraid it won’t attract many people.
And also, I need to sleep from time to time.
Was the cash shop useful ? Useless ?
I don't think this was used often enough. It was too attractive to keep "saving" for another life, instead of using it to send a malus to other users. Maybe add a 20% "storage tax" on all unused Bitcoin, for each round. So 50 BTC > 40 the next round > 32 the next round.
Yeah, I noticed the same thing (for the third life, seeing Leahized stuck at 97
BTC for so long really made me laugh). The Cash Shop needs a revamp, but I would have thought you would be more aggressive with each other.
Signing a message
is simple

I'd say go for this: Bitcointalk users should be able to sign a message and follow simple instructions.
I'm afraid we are underestimating the number of mobile users. Are there any Bitcoin wallets on cell phones that let you sign a message ? (I don't have anything related to crypto on my phone. I just use my phone to make phone calls.)
Otherwise, I was thinking about something : can you easily add another user to LoyceVs PM publisher, one you wouldn't have access to ? But one way or another, if you wanted to, you still have access to the data ?
Even if that exists, you'll get the complication of creating external accounts. I create as few accounts as possible.
I'm on the same page as you.