The applicable downsides that have been brought up are unfamiliarity with the equipment and basing a job off of new equipment that may or may not be working properly. If I have sufficient time to play with it before using it for the job I don't think those two will be issues. If there is a problem, I can rent a 50mm RB lens from Dallas Camera per David's suggestion below.
Thanks everyone for your responses. I may seem like I asked a question that I wanted a certain answer to, but I do value the responses and collective knowledge here. Aside from any general concerns about doing jobs with unfamiliar equipment, are there any other issues that may be a factor in deciding whether or not to switch to the RZ system from RB?