Two things I've noticed --

In your examples you're showing commands like --command:arg. I think it's more usual to see --command arg, ex dotnet build -v DEBUG --runtime win-x64. This is pretty minor though.

Secondly, you're sort of parsing two arguments in one go, and I think this will bite you going forward.

Take the following:
gitversion write --from:file=gitversion.json --to:assemblyinfo=./**/AssemblyInfo.cs

I think this would be much better represented as:
gitversion write --input-type file --input gitversion.json --output-type assemblyinfo --output ./**/AssemblyInfo.cs

It is certainly more verbose, but it gives the users and developers more flexibility when constructing their commands, and it stops you from inventing your own constructs as to how a command should look.

Array-like binding would look like:
gitversion write --output-type projectfile --output project1.csproj --output project2.fsproj

I used input/output as an example (and input-type and output-type sound better than from-type and to-type), but you get the idea

Thanks for the feedback @svengeance! I agree with you and will adjust my examples (moved to #2275) accordingly.