Why bother with the middle man? If Softbank is so confident that its vision fund is going to make much bigger than 5% returns, it should be putting the money directly into there.
This is a perk for employees. Stock options/RSUs on steroids. It’s nothing more complicated than that.
It’s unusual to do it this way in tech but in big accounting and law firms giving favourable loans for people to “buy into” the partnership is business as usual.