We could get between $6k and $7k annually per citizen by swapping those plans for a basic income. If children don't count, we could bump that to maybe $10k. Obviously, this change would need to be taken gradually to not cause too much disruption.
To hit that $20k number, we'd need to increase taxes. Increasing consumption taxes would be fair. Since the flat credits is very progressive, it's OK to pay for it with a regressive sales or value-added tax.
I'm glad we are in agreement that a BI will cost a lot more than the current targeted welfare state. (Or alternately will require a drastic cut in benefits for the current crop of non-workers.)
If you didn't earn any money before you will get what was spend on you before + the saved overhead (+ a lot of wasted time and hassle). If you made a lot of money before you will still get a free handout but you also have to pay higher taxes so in the end you should have about the same amount. Obviously it will not be exactly the same for everybody but that doesn't mean it will be less fair.
Besides the saved overhead another major advantage of a bi would be to streamline incentive. Currently it can happen that if you start earning money you will lose a lot of benefits. This can lead to an implicit tax rate of > 50% for very poor people and therefore disincentives work.
I'm completely open to the idea of basic incomes but it seems that if it is possible, it should be easy enough to demonstrate the basic outline. This isn't something that can be discussed without arithmetic.
Excluding dynamic effects (more/fewer people will work), political necessities (program X must be excluded from the chopping block) is OK for a start. Picking and choosing countries is OK for a start.
The first question I would like to see answered is how much it would cost to bring every net recipient's income up to par with the biggest recipients'. Presumably the basic income needs to be set somewhere near this line or we'll have a situation where many current recipients are worse off.