I was describing a simpler system for implementing UBI. You are right that I left out how to transition to that system.
For example, you could do more or less the same thing that the UK did to abolish slavery: buy out all the existing land owners / lease holders.
I suggested 20 years as a reasonable time frame for leases. In principle, 100 years might would also work. 999 years is probably far too long.
Now, instead of auctioning off the leases, you can also have individuals officially owning the land, but instead you tax them a certain fraction of the market value of the land every year. Economically that's equivalent.
A 999 year lease is basically economically the same as owning the land. So you should more or less treat it the same.
Or are you proposing State confiscation and management of the land? I can’t quite tell from your post.