For the past year, the BAT Slew Survey (BATSS) has been operational and surveying the high energy sky by utilizing the data from the rapid (~1min) slews of Swift between targets and (occasionally) to or from GRBs. Although slew coverage is limited by downlink and on board constraints to about 30-40 slews (out of ~60 total) per day, new GRBs have been discovered and new transients or flaring sources found. I will review BATSS and some of the results from its development phase and now operational phase as well as the sensitivity that scanning (vs. dithered-pointing) allows. The results are relevant for the proposed (to Astro2010) EXIST mission, which would include a scanning survey (2y) of a large area (4.5m^2) wide-field High Energy Telescope (HET) and sensitive Soft X-ray Imager (SXI). GRBs imaged in HET (to <20") would trigger rapid (<200sec) followup pointings of HET, SXI and a co- aligned 1.1m optical-Infra-Red telescope (IRT) to measure GRB redshifts and spectra in real time for the first systematic probe of the Epoch of Reionization (EOR). The followup 3y pointed phase of the EXIST mission would identify and study large samples of AGN and (potentially) Blazars at high-z as well as continue the high-z GRB studies. EXIST would be a joint US-Italy mission with significant discovery space for a wide range of investigations.