Playing at the BPA would require some form of investment to make it safe for L2 football. SISU simply have no money to make even a small investment on making the BPA suitable for L2.
In my opinion SISU have no credibility in the City of London so I don't see how they are going to raise any funds from outside investors.
WASPS will understand that SISU's threat to move to the BPA is a non-starter, so they will ask for a high rent from SISU for staying at the Ricoh. In my opinion, it's a race to see who will go bust first - SISU or WASPS. My money is on SISU to go bust before WASPS do.