I suggest you talk to someone at the university about it.
Honestly, I go to melbourne and they are sooo unorganised in regards to phasing-out the old degrees and phasing-in the New Gen that they probably won't know the answer.
Generally I believe when a course is being discontinued, you are not able to defer it - so you will have to start this year or not do it (ie. you should ask the university if you are actually able to defer a BEng). However, some courses, if the intake is large enough (ie. 1000 students will be beginning/offered BEng this year), there might be a high enough percentage of students wishing to defer that they allow it and run BEng first year subjects next year for those students to begin their course then. Otherwise, it is normally assumed that if the year is the last year that the course will have an intake of new students, the first year subjects will only be offered in that year, and in the next, only second and third year subjects, and in the third year after the last intake, only third year subjects will be available (if that makes sense). That allows the phase-out of BEng subjects to be over in 3 years.
But it all depends on the uni and the course, so I would really recommend contacting someone in the Engineering department or enrolements, and asking them for a yes or no 'can I defer the BEng?'
Hope that made sense/helps!