A squad size of 28 goes to the Jnr RWC.
Previously the functional breakdown of the young Men in Gold squad was:
2014 Squad (from Wikipedia):
Prop: 5
Hooker: 2
Lock: 3
Loose Forward: 5
Halfback: 2
Flyhalf: 2
Centre: 4
Back Three: 5
Pigs: 15
Princess: 13
Squad: 28
2013 Squad (From G&GR Blog archive):
Prop: 4
Hooker: 3
Lock: 3
Loose Forward: 5
Halfback: 3
Flyhalf: 3
Centre: 2
Back Three: 5
Pigs: 15
Princess: 13
Squad: 28
@Sideline Eye suggests that the selectors are likely to follow a 3 hooker squad like 2013, which would be good for connections of the 6 hookers at National Champs, and the @Sideline Eyes are possibly checking passports, and annual leave and bank balances just in case.
Tournament play is often about survival of the fittest, and consequentially selectors usually look for players who can play more than one position over a specialist. The hooker that can prop, or can play OSF. A prop that can play LHP or THP, or hooker. A lock that can play #8 or BSF. A halfback that can play #10. #10's that can play #15, Centres that can play wing etc.
In addition to @Lee Grant's fine preview above, I'd think the selectors will be looking for those who can play multiple positions. They will also be looking for a left foot kicker, both from the tee and the hand. It will be essential that we can bank on 3 points for any penalty given 45 metres (centrefield, or 40 from the side) from the posts (if we want to take the points), or a 5 metre attacking lineout for any penalty awarded anywhere in the attacking 1/2, not to mention a Red zone exit kicker that can reliably return the Gilbert to the far side of the 10 metre line (if not 1/2 way).