They'll probably start that way, but will add more features closer to a 1.0 release.
Every one of their IDEs starts simple and then develops to one of the best in the industry, I don't see why this should be any different with Go.
Best in the industry? I wouldn't go that far. Considering how slow JetBrains tends to be with fixing bugs (I logged a few against PyCharm in 2011 that still haven't been fixed, which is why I don't use it anymore), how unstable their environment can become when debugging, and how they refuse to address Dvorak key-mapping issues in macOS, I think the furthest I'd be willing to go is that JetBrains makes some IDEs.