Ukraine dont have the money to go for Western design. Where can you get a decent modern advance trainer that can filled training role/attacking and fighter intercept role ,all in one w/o burning a hole in yr pocket? China, L-15b. Not to mention the engines are deprived from Ukraine will even simplify more process.Eh, do they even need one anytime soon? If the do I think they would go for a western aircraft due to changing geopolitics in their tension filled area.
The only obstacle will be selling arms to Ukraine may raise objection from Russia who is a strategic allies who deemed such move is provocation since it may use those plane against Russian.