I feel like there really wasn't enough solid info given to really say anything about it. They said that your concerns would be similar to Bard (pseudo support) but different specific things you'd be worried about.

So there's "Ammunition" stacks, which you get 5 of for using Reload. Are you required to have them to use any/certain weaponskills? How frequently can we use the Reload and Quick Reload, which gives 1 stack instead? Vague mention of some unspecified bonus for reloading while you still have Ammunition stacks that have not been used. Said that you would want to use downtime in fights to reload.

Something mentioned about some stacking proc buff but it was incredibly vague. Using "Shot 1", then "Shot 2", then "Shot 3" gives increasing % chance of this proc but no mention if those are specific weaponskills, weaponskills from a particular group or just any gun-based weaponskills. No mention of what this proc buff does or what it affects.

Turrets were mentioned in passing and all we really saw was one deployed and auto-attacking an enemy. Supposedly grant some kind of buff/debuff around them but nothing mentioned or shown in regards to that.

Bombs were mentioned as weaponskills, one was shown in the video. No mention if there are any mechanics that affect them.

The previously mentioned attachments saw absolutely no mention in the Live Letter and previous info on the system has been incredibly spotty at best.

Honestly, I just don't think there's enough real info to go on to predict much about them.