Praise be to Allah.
We put this question to Shaykh Muhammad ibn Saalih al-Uthaymeen, may Allaah preserve him, who said:
This (i.e., adding something to the price of the land) is a payment for handing over his turn with the fund.
Doesn’t this reward for handing over his turn involve paying for something sight unseen (majhool = unknown)?
No, it is for something that is his. He may or may not get the loan, but both of them are taking the same risk, the one who is handing over his turn and the one who is taking it from him.
So what is the answer?
The answer as it appears to me is: there is nothing wrong with it if the state (who owns the real-estate fund) allows it.
And Allaah knows best.