There's a lot of merit to this IMO. Foursquare the brand is completely and 100% associated with checking in to places. It seems silly to break the checkin feature into a completely new app, under a completely new brand, while trying to convince everyone that Foursquare is no longer Foursquare but is stilled called Foursquare.
IMO the better move was to keep Foursquare around but launch a separately-branded app for the discoverability.