I think that in 20, 30, 40 years' time, automation will have transformed the world of work to the extent that there will be no alternative to something like UBI or some such scheme. Look at the prefab houses on the UKIP thread, or the transformation of car factories (I visited the Skoda plant outside Prague a couple of years back - hardly anyone there but producing cars by the thousand), supermarkets will doubtless be entirely automated in the not-too-distant future. Even in my own little world of translation, machine translation is already changing the landscape - can't really see the profession of translator existing in 30 years time.
The capitalist imperative will force businesses down that road so less and less people will be employed at all, but, in theory, profits should increase as costs go down - which in turn (bear with me on this bit, it's a bit fanciful)... should lead to an increase in tax take (I know, I know...) Would that increased corporate tax take (stop laughing) be enough to fund UBI in some form?