Get rid of commendations, Level 31 gear could only be bought:
A: if you beat VoG (majority of Destiny players haven't)
B: are level 30
C: iron Banner gear
Alternative RNG based:
D: lucky engram drop (but the cryptarch won't budge anyway)
Old gear would still be sold and there would be a new tab (L/R bumper) to change to the new gear. No commendations needed for old gear.
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Personally, I think that vanguard gear should only get you to level 30. Getting to 31 with gear that can be bought is a bit ridic.