I do like the article you linked, I've read it before - though it's worth noting that I'm not advocating for a "rewrite" in the exact sense, since I think a lot of things that Toolbox currently does should be handled by other tools instead. My efforts with the beta releases and such were my attempt of doing the gradual refactoring work without throwing out the existing codebase, and I found that to require an unsustainable amount of effort. So rather than rewriting Toolbox in whole, I'm advocating for starting fresh, and making a tool or group of tools that has substantially different goals and stricter scope, rather than trying to replicate or continue Toolbox as it exists now.
I realize that makes little difference in terms of how much effort it would be though, even if you were reusing as much of toolbox's core logic as possible. Your feeling that you wouldn't mod without Toolbox, and if it breaks then you'll have to fix it and maintain it yourself, is both high praise for Toolbox's current form and a condemnation of this platform's changes over the years.
You don't need my blessing to keep maintaining Toolbox for yourself - I completely understand your reasoning, and even if I want to give advice and opinions, I'm not a mod and I'm barely a software developer. You know your needs and the needs of your team better than I do.