Will this be fixed in 6.x?

While, I am very interested in implementing this feature, no customers have expressed interest in it. Other issues with higher priority remain to be resolved in WiX v6. That is why this issue is in the v.Future milestone and is not likely to be a part of WiX v6.

As the original author of this thread, I am still interested...

We are interested as well

I am also interested. I have manually added support to my project with these lines:

<PropertyGroup>
   <!-- WiX SDK doesn't follow UseArtifactsOutput, apply it manually -->
   <ConfigurationLower>$(Configuration.ToLowerInvariant())</ConfigurationLower>
   <PlatformLower>$(Platform.ToLowerInvariant())</PlatformLower>
   <ConfigurationWithPlatform>$(ConfigurationLower)_$(PlatformLower)</ConfigurationWithPlatform>
   <OutputPath>$([MSBuild]::NormalizeDirectory($(ArtifactsPath), 'bin\$(MSBuildProjectName)', $(ConfigurationWithPlatform)))</OutputPath>
   <IntermediateOutputPath>$([MSBuild]::NormalizeDirectory($(ArtifactsPath), 'obj\$(MSBuildProjectName)', $(ConfigurationWithPlatform)))</IntermediateOutputPath>
</PropertyGroup>

However, this isn't a complete solution. For starters, I believe it only works with an explicit ArtifactsPath, not with the automated UseArtifactsOutput property.

I recognize that it may be too late for WiX 6, but I am willing to implement this myself and give a PR for WiX 7, if the team is interested.

@brantburnett you're welcome to dig into it. Integrating this support into the wix.targets is something that I'll need to understand deeply, so be aware I'll go through the development myself and may not use provided PRs. But that isn't to say that they wouldn't be helpful. :)