I'd like staff as a long range weapon. I'd rather go for power-oriented support weapon as in my mind it would fit well with a staff on engineer. I would go for offensive support rather than healing because if Anet would just buff our core options like Med Kit and maybe change EG 5 to a water field we'd have good healing support already. If I'm thinking in a real sense though I would bet the next weapon will be a mace, either mainhand or dual wield, and it will be a condi based support spec. Since both current elite specs are power bruisers/damage oriented, that leaves conditions and support, and Anet has already made 2 specs that combine both with Firebrand and Scourge.