Pretty much spot on description from the SA forum, hell even The Sims Online used an API in the exact same way between the clients and server. If you want a real challenge try doing that in an open world online racing game. As he mentioned in his post, timing and order are everything.
These are not new techniques, in fact I would say it's a little outdated given languages like Go handle this a lot better.
I found the token idea enlightening and remarkable, it's a very interesting direction to go in too. Constructively I see three potential pitfalls:
1) Taking into account tokens on AWS - depending on the size of their EC2 instances that it becomes a very difficult to filter out the noise between a MA (master server) and SA (listening servers), if you have five servers, four being listening servers then by definition those servers will be getting traffic from clients (except for the master server if you have any sense), if the token switches that means that server will have to drop all client data and then dynamically reallocate the clients to the server that has passed on its token. If all five servers are sending and receiving traffic then the master effectively becomes swamped with clients at the same time as losing its token = chaos. TL;DR if they do use tiered servers with tokens and dynamically switching it will be very difficult to maintain consistency, if they don't then they will run into bandwidth issues anyway.
2) Why are they attempting to reinvent the wheel? There are already third party engine modules of CryEngine that handle this already in a pre-built form? This means a lot of time has been used for something that has already existed off the shelf for ages, if it doesn't do what they want it to do they could very easily modify them, they're open source or licensed models provide the source.
3) This is adding another layer to their engine, at this point with so many layers how will they debug? They mentioned it in the video but now you run into the issue that the client (or one of the clients) may not necessarily know which server has the token (or if there are connectivity issues) in which case it becomes more difficult to troubleshoot and diagnose. This is not bad within itself if you have a custom toolset for debugging issues written for your platform, but again you're adding time creating one. Thus more code to maintain (refactor as CIG likes to say) from revision to revision of the custom written network stack as part of the custom written modules as part of their bespoke engine (Star Engine or Lumberyard with heavy customisation). More techdebt.
Yeah. It's all rubbish really.
Here is another good write-up by Hav, over on SA.