Our client library is entirely open source, but our platform itself is not as it's a commercial no-backend offering. This allows us to offer production-grade hosting for these types of no-backend apps.

Many companies offer production-grade hosting for open source applications. The fact that you are keeping your source closed tells me that you are afraid a competitor (or your clients themselves) could achieve an equivalent quality of hosting for less than they would pay you. To a customer like me, this is bad news.

We absolutely think that open sourcing code is important, but not just a giant lump of all of it; a mountain of code not always useful.

It's still early days for us but we are considering open sourcing reusable parts of our platform or allowing people to host their own if they wish, but we haven't yet decided on which we will pursue yet.