When it comes to stagnation and development, which would you choose? I'd go for development and that's what we're most likely to get here
I addressed that. Monopolists don't like development. They progress only when pressured by competition. Steam Machines are one contender, but most here dismiss them as insignificant. So, where do you expect the development to come from?
As for the real modding, you have some funny ideas there.
Nothing funny here, it's a pretty basic idea actually, of what non restrictive platform should be. You can compare it to freedom of speech / expression, in artistic or technical context. And DRM of console gatekeepers to censorship tool. And how console incumbents react to real modding, you can see here: https://en.wikipedia.org/wiki/Sony_Computer_Entertainment_America,_Inc._v._Hotz