apiinfo.version currently returns 1.4 in 2.0.0.rc3. Perhaps this would be a good time to bump the version to 2.x. Two thoughts come to mind:
1) x.y.z where x.y follow the first two numbers in a Zabbix frontend revision, and z is incremented only when a change is made to the API.
2) x.y where x is always incremented with every major zabbix release 1.8, 1.9, 2.0, 2.1 2.2 etc, and y is incremented only when a change is made to the API.

I'm leaning towards option 1 as it may be a little easier overall to maintain.