The longer it takes to enact UNSC reforms the lower the chances of SC expansion with veto powers for the new members. People have mentioned Germany and Japan as being interested, but there are several second tier nations (Turkey, South Africa, Argentina, Arab States, ASEAN members etc.) that are developing rapidly and will gain more and more clout internationally and will either start demanding a stake for themselves or opposing the extension of discriminatory privileges (veto) to a select few more.
True SC reform would involve the removal of veto powers from the existing members, not increasing members with veto powers, something along the lines of the what the Coffee Club is proposing. More members with veto is a recipe for inefficiency and logjam in the SC, given that the number of competing interests will increase by many magnitudes, and any one of the nations could halt progress on issues brought in front of the UNSC.