I think he simply means that there is no point in providing three copies of each identity card in an expansion. Assuming they recognise this (and the format of the core set suggests that they do), they will only put in one copy of each new identity card, which leaves unused slots in each 60 card expansion. These slots cannot be filled by non-identity cards because they have said that all other cards will come in threes. The most effective way to deal with this would be to put three singleton identity cards together in a single expansion, with 19 other cards appearing three times.
However, if each faction is getting a new identity, that is at least seven identities. Assuming they follow the obvious pattern I suggested, it means that there are two unused singleton spaces that cannot be used for non-identity cards. I therefore assume that some factions will be getting more than one additional identity.