FYI, LBaaSv2 is the API specification implemented by both the end-of-life neutron-lbaas[1] and Octavia.
Both values are dependent on which driver you are using. Some drivers have limitations that other drivers do not.
I can't really talk to the limitations of the individual neutron-lbaas drivers.
If you are using Octavia instead of neutron-lbaas, the maximum number of members is dependent on the amount of RAM allocated to the amphora instance. We understand one user has a pool with about 400 members in production with stock settings. At some point as you approach 65,000 members, the performance of the member servers will impact the ability to service the health checks in a timely manner, however you could disable health monitoring to bypass this. Octavia also allows all 65534 ports for the VIP.
[1] https://wiki.openstack.org/wiki/Neutr...