The story itself admits the limited coverage. The Russians have not risked their air force much but most of their tactics favour the use of long range missiles and drones, anyway. However, the VVS is being upgraded in the meantime and they have developed their own new gen fighter already. Whatever, any NATO warplane activity in Ukrainian skies may well produce the same reaction from Russia as any NATO boots on the ground might do. Risky without any prior agreement, at least.