IMO, VSCode's codebase is excellent and quite well designed with most functionality abstracted out into injectable services. However, the interaction of these services and other bits of architecture do impose certain limitations that are tricky to workaround. One option is to fork vscode, write your own services, alter the architecture as necessary. You're then faced with keeping this in sync with the rapidly changing upstream code. Another alternative is to implement it as an extension, but that has a fair number of restrictions.

For certain projects, forking/extending may be the right call. However, for the degree of customization required for Scripton, writing from scratch turned out to be the more viable path (vs attempting to workaround/rewrite yet another component in vscode). The trade off here, of course, is that you lose out on the familiarity and ecosystem that VSCode has built over nearly a decade. The hope is that Scripton remains sufficiently familiar (eg: Search / CMD+P / etc work similar to vscode) while being compelling enough in its own right.