Is the idea of “loose open core” that the commercial enterprises attractive to VCs live in the ecosystem around a free-software core, whose developers are funded by fellowships from the ecosystem?
Can an orbiting comercial entity be large enough to attract VC-funding when the core functionality is fully free? If not, it’s no solution. However, if the add-on commercial functionality is substantial, can the software be no longer called open?
My solution: A near-FOSS licence that drops Freedom Zero (the freedom to run), but keeps the much more important ability to fork, modify, and re-release. When a licence to use a fork is sold, the owners of that fork must charge at least that charged by the version from which they forked to run the version in a production context, optionally adding their own premium. In this way money percolates towards the root of the fork tree, properly funding each contributor according to their value-add, while still giving everyone the power to customize (the true value of open software).
So libre not gratis.
To respond to your “Open software avoids cost lock-in” point: Run charges don’t have to be per core or per seat, but should still be able to vary according to the type of user and the size of deployment.