I don’t believe I-73 should ever be built. It’s not needed. You have alternatives; you have U.S. 501 on the south end of Myrtle Beach and S.C. 9 on the north end.
Improvement of these roads would serve the same purpose and then some.
Also another alternative is try to get together with North Carolina if possible. Expand S.C. 31 north and tie into U.S. 74. If you can make that happen you would save lots of problems east and west, north and south. That will make you forget about I-73 and the political pockets that it would fill.