Going to try to reason through out choices here.

First, we could forcibly track HEAD for dependencies pointed at a branch for each build. This has the benefit of making builds (mostly) reproducible since you aren't going to be building against stale versions of those dependencies locally then, when CI clones the latest, the build fails (best case) or (worst case) it succeeds but there are bugs you do not see locally. The drawback of this choice is that it lengthens development cycles when dependencies are following a branch. Maybe that's just the price one pays for following a branch.

Second, we could create a separate command where one must actively choose to update dependencies to build against the latest HEAD for their tracked branches. I think it's unlikely that this would get much use until someone has already possibly lost some time to fighting a dependency issue or wonders why they aren't seeing upstream changes from one of their deps. It would make the dev cycle theoretically faster for some savvy folks though.

I'm really leaning towards the first option. Maybe slower development cycles are just the price you pay for chasing a branch. I would rather gopack be correct than fast. And if someone is really concerned about speed they can always pin to a tag or commit.