Gene therapy is an active area of research; most gene therapy approaches that are studied use some sort of viral vector, those that don't are more the exception and it is unclear how several of those methods would be applied clinically.
There have already been clinical trials of gene therapy with viral vectors, with mixed success.
Edelstein, M. L., Abedi, M. R., & Wixon, J. (2007). Gene therapy clinical trials worldwide to 2007—an update. The Journal of Gene Medicine: A cross‐disciplinary journal for research on the science of gene transfer and its clinical applications, 9(10), 833-842.
Ginn, S. L., Alexander, I. E., Edelstein, M. L., Abedi, M. R., & Wixon, J. (2013). Gene therapy clinical trials worldwide to 2012–an update. The journal of gene medicine, 15(2), 65-77.
Greenberg, B., Butler, J., Felker, G. M., Ponikowski, P., Voors, A. A., Desai, A. S., ... & Pogoda, J. M. (2016). Calcium upregulation by percutaneous administration of gene therapy in patients with cardiac disease (CUPID 2): a randomised, multinational, double-blind, placebo-controlled, phase 2b trial. The Lancet, 387(10024), 1178-1186.
Kay, M. A., Glorioso, J. C., & Naldini, L. (2001). Viral vectors for gene therapy: the art of turning infectious agents into vehicles of therapeutics. Nature medicine, 7(1), 33.
Mulligan, R. C. (1993). The basic science of gene therapy. Science, 260(5110), 926-932.
Naldini, L. (2015). Gene therapy returns to centre stage. Nature, 526(7573), 351.
Niidome, T., & Huang, L. (2002). Gene therapy progress and prospects: nonviral vectors. Gene therapy, 9(24), 1647.
Thomas, C. E., Ehrhardt, A., & Kay, M. A. (2003). Progress and problems with the use of viral vectors for gene therapy. Nature Reviews Genetics, 4(5), 346.