The problem with the UG is that it, too, doesn't have the creditworthiness of a "real" GmbH - and we're back at square one, no viable way of getting capital except by putting up personal property as collateral.
So the real problem is not that it's not possible to have cheap company with liability protection, which UG suits perfectly, but being able to borrow money / get investment for a company worth 0€. Those are two totally different things.
That's why we now have the "small limited" company (Mini-GmbH or UG). You can start a company with limited liability with just a few bucks^H Euros.