I believe interpretation B is superior to interpretation A for several reasons, but the following three are the most important:
1) In Rom 9:6-9, Paul is returning again to an argument he already made in Rom 4:9-16: the true heirs of promise are not merely the physical descendants of Abraham but rather all who follow in the faith of Abraham.
2) Paul argues in Rom 9:10-18 that election is independent of works, but he never argues that election is independent of faith.
3) Paul will state explicitly in Rom 11:7-14 that those individuals who are currently “hardened” and not “elect” may still be saved. This affirmation is irreconcilable with interpretation A.