Why? Ukrainians nation was created by Austria after 1866 to counter poles,before it was just few students.Tsar have nothink to fear from them.What if Russia decides to flood Novorossiya with Russians (formerly known as Great Russians) starting from the late 18th century onwards, viewing Little Russians (aka Ukrainians) as too unreliable for this task due to them previously being ruled by Poland for several centuries?
They could start it after ,let say,1880,but dunno if that would help or not.
P.S Sralin after genociding part of people there send new settlers,so,in a sense,it was done.