Yes the option to embark troops was already here, but as @Abburo said, you can now trigger it via the Comm menu while inside the vehicle. As @Flappie said, I saw many inconsistencies (bugs?) which will not be qualified until we have a proper description of this new feature. To be honest, I'm a bit disappointed as I thought it would be a first step towards a Combined Arms enhancement which seems necessary before CH-47 and C-130 release, and today, I don't see the point of putting such a "minor change" ( from what I guessed, perhaps I'm wrong ... ) in 2.9.
Time will tell... ( I'm currently putting together which basic features I think would be needed to enhance ground combat, would probably submit the ideas to @Flappie when done )
NB : Also add the flying APC bug when trying to embark in an IFV whith 0 place left. The marine bumped it 10 meters up