The potential pros of shuttering FINRA and PCAOB include streamlining regulatory oversight, cost savings, increased accountability and transparency, and greater Congressional oversight.
Possible drawbacks include loss of specialized expertise, overburdening the SEC, regulatory gaps, and industry pushback. Many industry stakeholders may fear that a more centralized regulatory body could result in tougher regulations or a more rigid enforcement environment under the SEC compared to the relatively more flexible and specialized structures of FINRA and PCAOB.
The success of such a move would largely depend on how well the merger is managed and whether the SEC can effectively handle the expanded responsibilities.
Full contextual analysis of Section 5.1: Financial Regulatory Agencies here.