We've added support for the .tofu extension and are working on IDE support for it. This will allow module authors to include support for new OpenTofu (and Terraform) features side-by-side. We have some good examples in the blog post!

In the mean time, OpenTofu is aiming to implement many of the new features that Terraform has been adding (driven by community input). We've also seen recent Terraform releases add features that OpenTofu has already included (templatestring for example).