The latest version gvm listall offers me is go1.4.
Am I missing something or is gvm outdated?
What's the recommended way to manage (potentially multiple) installations?
Yes, please update gvm. Also note, there are still some issues with Go1.5 and GVM, look at github.com/moovweb/gvm/issues for tips.
$ bash < <(curl -s -S -L https://raw.githubusercontent.com/moovweb/gvm/master/binscripts/gvm-installer)
$ source /Users/vasi/.gvm/scripts/gvm
$ gvm listall | grep 1.5
go1.5
go1.5beta1
go1.5beta2
go1.5beta3
go1.5rc1