likewise, I'm building a social-network-y site for retail investors (https://www.holfolio.com) to track and share what they and others are investing in.

One of the main points is you can see the history of what someone has invested in and get a picture of their whole portfolio. Some people currently post their trades on traditional social media but its really hard to keep track of, these fleets are only going to make it worse (helping me in the process?)