The following are mayor risks in this area
EaaS have many flavors, and of course the risks might change significantly based on the exact flavor, in some situations the EaaS quote to bill might be based on self-service order and be completely automatic, in orders each quote is negotiated individually, etc. of course the risks change drastically depending on the different scenarios. The list above represents my best bet without knowing anything about a specific case. Of course in real life we should do a risk assessment before deciding what are the principal risks.
I agree with you that there is are not well defined RA best practices for the EaaS. It would be great if you could join the TM Forum Business Assurance team, and contribute to create it.