I'd only really entertain the idea if these AI optimists are correct about AI and robots doing literally everything. I assume they are wrong, but having a system in place before it becomes a crisis seems wise. That's why I like the idea of being able to turn it up or down. Start with it way down, basically off (during this period, maybe the funds collected go toward shoring up social security). If things get bad, turn it up, and if the market starts to adjust and new types of jobs are created, turn it down again... so it can serve the purpose of bridging the crisis, rather than having congress issue checks randomly like we say 5 years ago.
To your point, how funds get distributed could be up for debate. Maybe instead of sending them to everyone, some kind of productive work that benefits society is required, and the fund would provide a way to get paid for work that normally pays little to nothing. The problem with this, is that the administration of such a program is expensive, error-prone, and full of bureaucracy, just like most other welfare programs. I'd like to think something like UBI would replace most of the other programs, to dramatically cut administration overhead for the countless programs that exist today.