The problem with the initial idea is quite circular, much like many other problems when discussing alternate history. This is, generally speaking, why many such matters did not happen.
The specific problem, as others have mentioned, with urban civilization in the Urkrainian plains is that the area is tailor made for nomadic societies, who tend to have a military edge most of the time. Some settlements might be able to prosper along the major rivers, but they'd still be quite vulnerable to nomadic raids.
Of course, the one thing that changes that irreversibly is the development of reliable firearms. Simply discovering gunpowder earlier won't help; the Mongols themselves used gunpowder weapons. You need proper firearms. Which requires earlier technological developments on a wide variety of fronts, most notably chemistry and metallurgy.
Such development would negate the desire for an 'earlier renaissance.' History is generally too interconnected for simple 'cause and effect' scenarios to happen in a vacuum in such a fashion. Suffice it to say, the effects you're probably looking for from an 'earlier renaissance' are actually the causes that would enable such a development.