We did a lot of testing in low speed wind tunnels with airplane models smaller than the one you are talking about! Typically for full scale airplanes that use the all flying tail in pitch and roll and they are sized for maneuverability at supersonic speeds where the aero effectiveness is quite low. This usually results in a lot of control authority available at low/model speeds.

For your question ignore the length of the fuse and just look at the elevator chord as a percent of the tail chord. If it is normal (less than 40% and greater than 20% or so) then it would probably be OK for pitch. Might not be too good for roll though. Certainly wouldn't look right :-)

All that being said for a scale model it would seem that the all moving stab is doable and desireable from a scale standpoint. Certainly the numerous F-4, F-100, etc flown in scale work today would indicate that the mechanics of the tail pivot are well worked out.