Being blindly optimistic towards a level cap increase when it has caused problems the last several times it's happened is foolish, you can't dismiss obviously bad decisions with "DOOM".
How many Shrouds or Abbots (Mark of Death doesn't count... and even if it did it barely gets run too) get run anymore? Caught in the web? Old endgame/raids get left in the dust every level cap increase, it's not just raids either tons of content just gets completely ignored because it's gear is no longer relevant, even slavelords is basically obsoleted by sharn.
And really the obsoleting of content is the smallest problem with a level cap raise, the population as it is is horribly spread out over 30 levels right now, adding any more will only worsen the problem of dead LFM. A server merge or crosserver play could alleviate this issue but if we don't get that then I cannot support anything to make grouping even harder than before.
While It's perfectly possible for them to pull this off and make it work... I highly doubt it given Turbine/SSG's track record.