I think the Greens have said that nobody will be worse off under their universal income scheme but you are quite right, those with say a severely disabled child would ordinarily lose out. If nobody is to lose out, which seems like a costly admin process to calculate, then there are fewer benefit savings to fund it. I think trial schemes have often targeted specific groups and shown it can be beneficial. If given to everybody it probably would be a net positive in countries where they don't have an extensive benefits system already in place.
		
		
	 
Well, they would say that wouldn't they?, particularly since the possibility of them having to deliver are not exactly high.
In a situation where nobody was to be worse off, the Universal income would need to be a lt more than £12k per annum, or, it would be necessary to have 'exceptions", so, we could begin building a byzantine benefits system again 😊
There was, or perhaps still is a trial of this (universal Income, at £1600 per month, or £19,200 per annum), in a Town near me 
https://www.bbc.co.uk/news/uk-65806599 it has all gone very quiet, so, I have no idea what the outcome was. I was in Jarrow today, I did not notice any visible affluence (although, the lady infant of me in the Morrisons Cafe Queue did spend £25 (after vouchers deducted) on three breakfasts 😊 Off topic, but, I also noticed that the "free refills" of hot drinks had been restricted to exclude Hot Chocolate, apparently due to some Government edict (I would guess the restrictions on "special offers" of unhealthy products).