If a model 1 seller registers under Streamlined, does it mean it will be contacted for audit by all fifty states?

 No, any audits would be performed through the CSP.  The individual seller would not be contacted by any individual state.  The purpose of the SSUTA is to reduce the burden of tax compliance for sellers.  Streamlined’s goals are to ensure uniformity across states in registration, sourcing of sales, exemption administration and tax return filing.  One of the intentions of Streamlined is to limit the intrusion of auditors on sellers.