There is a small gotcha here. --install supports installing from file shares and NuGet, correct? However, as we discussed, in the future it may be a lot more potential sources. It will get tricky because for some of those sources the --version will not make sense. We need to sit down and design this somewhat. :)
Today we support --install to a NuGet package or a folder. Later we may add sources like git. As you stated in the NuGet case we can have a --version and in the git case we may have a --branch. We'll have to figure out what's the right experience for this. We can chat more next week when we meet.