Day by day people are getting to know crypto currency, each day good number of interested people join the BitcoinTalk forum. The way the bounty qualifications and rank was in 2012 is not any more. Getting to the next rank is getting more difficult,KYC came in and many other changes, Now don't you think very soon most signature will only be opened to people from Full member and/or very few number will be given the chances of participation in many bounty campaign to have it convenient?
In addition to that, bounty hunting isn't yet as profitable as a few years ago, because the number of legitimate ICOs is decreasing with time, and the altcoin's market is still struggling. So I believe that yes, with time the number of bounty participants will decrease for sure.
Its already been decreased wayback before but there are still a few which do bounty hunting hoping for some jackpot on earning some decent money out of it but we know that numbers of legit projects can already be counted with our fingers and finding the legit one wont really be that simple or easy.
Im not saying that its over for ICO bounties now but it seems that it is already heading that way.