I mainly use Ardour as an arranger because of a comfortable workflow. I don’t use it for DSP though because what I do (sound for picture) doesn’t really require real time processing so I don’t see it necessary to download LV2 plugins. And a big project with at least few effects on several dozen tracks each would be really resource intensive. So in my case I rather prefer to process a file once using command-line programs like SoX and then leave it be.
What I have in mind is a feature that could export a region, open it in a external application and then replace the same region with an edited/processed one. This could either work with CLI tools like SoX or even more advanced utilities like Audacity for more advanced audio editing (I’ve seen few posts here suggesting more advanced editor within Ardour - maybe this isn’t really a solution but it could be at least more convenient for those people as well). Traverso-DAW has a feature like this and I think it works really nice so I’d really love to see it in Ardour.