After a few months of limbo, the official position on motorcycles using the new "ExpressLanes" on I-110 and I-10 has been clarified: we can do it, free of charge and without a transponder or FasTrak account. Yay.
Motorcyclists who had purchased a transponder for that purpose recently received this email from Metro ExpressLane Customer Service:
"A recent improvement to our tolling software now enables motorcycles with a standard issue license plate to travel on the Metro ExpressLanes toll-free without a transponder or FasTrak® account, effective immediately! This is based upon the DMV issuing unique license plates for motorcycles, coupled with a software improvement that now allows us to positively identify a standard issue motorcycle plate. If you would like to close your account, please return your transponder with a note that you would like to close your account."
The news is verified by the Orange County Register as well.