Open core is definitely a tension (disclosure: I work at Grist). Specifically for Grist, we differentiate by offering data portability and autonomy, and a full-featured open-source app is part of how we do that. I invite you to check the repo out, you'll see we're not holding back. We did want to flag the project as open core from the start, since we will build proprietary services and features around the core app (which again is very featureful!), and don't want that to come as a surprise down the line.