ignoring the point that God does not only give the promise for one time only and he is no a respecter of persons, meaning he does not show favoritism towards anyone.
Sure he does, he shows favoritism to his people, meaning the Jews. He makes that perfectly clear throughout the OT. He doesn't necessarily show favoritism individually withing the Jewish community, but as far as his preference, there is no doubt about who his people are.
So now you are asking for where scripture says God has a "plan for salvation"?
Not really. The only reason I mentioned salvation is because the so-called "plan" and "purpose" (actually boule, or counsel, in Greek), is understood by the Christians as having been the Grand Plan of God's form all eternity, namely the salvation of the elect, and Jeremiah's verses definitely do not point in that direction.
I am just curious why would God create a sinless world, let it fall, just so that he can restore it again with blood an guts. Doesn't sound like a great plan to me.
At any rate I can think of a few verses, where boule occurs, such as Luke 7:30, implying that God's purpose was to baptize the Jews by John the Baptist, which is unsupported by anything in the OT= because the OT God does not require baptism but circumcision.
Or in Acts 2:23, 4:28, 20:27...a clear pattern emerges, namely that it is Luke's innovation because nothing like it prefigures such a thing in the Old Testament.