Small Business Modernization Act of 2004 - Amends the Internal Revenue Code to: (1) terminate subchapter S corporation elections after 2004 and subchapter S status after 2014 and to allow privately-held domestic corporations, in lieu of electing subchapter S treatment, to elect to be treated as partnerships for tax purposes; (2) set forth rules for the tax treatment of former subchapter S corporations electing partnership status; and (3) exclude from net earnings from self-employment partnership income attributable to capital.