I'd assume that even though it's not a home nations bid the RFU will use the Principality Stadium and possibly Murrayfield for some matches like they did in 2015.
IIRC, there's an agreement dating back to the 1999 RWC that the home nations will share matches around, but it also makes sense in terms of maximising the fanbase. The 2015 schedule was clever with Scotland's matches at St James Park, Wales and Ireland in the Principality for several matches and France and Italy in the London Stadium (convenient for Eurostar and the short hop to LCY)