What concerns me somewhat about Pulumi is we will lose some of "standardization" that comes with the widespread use of Terraform.
Like anything else, it is possible to write Terraform in an incomprehensible way. However, overall I have found that Terraform "constricts" things into being done a certain way. This allows engineers to jump into a new TF codebase and grok what is happening fairly easily.
Now with Pulumi, we lose that constraint, and now have to grok not only the different languages that infra is defined in, but also the wide variety of different "styles" that a language can be written in. An engineer joining from another company or team now has to deal with a new language and a new code style/organization in order to wrap their head around the infra. Not a desirable property when it comes to managing the infrastructure for a company.
While it is appealing that a developer can use a language they are already familiar with to manage infra, that only holds true if the language being used for Pulumi is one they are already familiar with.
I could of course be totally wrong. Regardless, I am excited to see a new contender in the space.