Does the GUIDE function miss in octave?
Correct. While Octave is compatible with many of the manual Matlab GUI creation functions, compatible GUIDE functionality has not yet been implemented.
If so when it gets implemented?
This has been discussed for several years. There are currently limitations to Octave's ability to handle certain types of function callbacks that it seems GUIDE created UI's make heavy use of. This would likely have to be solved before MATLAB GUIDE produced UIs would work directly in Octave. Of course, there are also a number of GUIDE specific functions that are not a part of the older UIControl set that would have to be implemented as well.
In short, it'll probably be a while. someone would have to solve bug report 39257 [1], which is a significant code undertaking, and then take on the GUIDE code development.
Are you interested in helping?