I cannot get version 3 of Math to work with a local installed Mathoid.
version 2 connect to a local installed Mathoid without problem (although there are display/viewing issues in internet explorer/chrome).
Version 3 seems to require $wgFullRestbaseURL, without this there is an error indicating this setting is missing. Math 2 does not have this problem and can connect using only the $wgMathMathMLUrl