Yeah, that upper management making decisions thing was the case when I quit my last job, and they had many of the other issues as well, just like almost every company seems to have nowadays.

Have you ever thought that people like you are the described problem for the rest of us?

Package Control is open source and a third-party extension manager. There's still nothing stopping you from writing your own package manager, but package control is excellent and I doubt there's much need to write your own from scratch, when you can just fork it, implement whatever extras you want and submit a pull request on github.

I doubt ST would be any better if the core app was open-sourced, because some projects stay better focused as one-man-jobs.

There are, however similar apps to ST / ST clones available as foss, like LimeText, Atom and ironically TextMate, which ST started as a cross-platform alternative to back when TextMate was closed-source and cost about the same as ST does now.

Still, I can do all of that with Sublime Text as well, and more. It even comes with a package manager to customize and keep updated the huge set of community-developed extensions. So, to list the equivalents in ST:

• Runs locally, but works with remote cli proxies; subl is the local host proxy app and rmate or rsubl remotely over SSH sessions. Running the editor locally isn't a problem, because I use exclusively my laptop for all computer tasks.
• Is lightning fast on my laptop; not a problem resource-wise. I haven't tested on an old i386, but I doubt I'll ever will have that need.
• Has a huge extension community as well.
• Is easy to configure via its .sublime-settings files, which are just plain JSON.
• Has syntax-highlighting, syntax-linting and general syntax-awareness like automatic indentation and block awareness for indentation keywords, parentehes, braces and so forth depending on the language for every language I've edited so far, although some are maintained by the community and are installed with the built-in package manager.
• You can do exactly that in Vintage mode, or do something like cmd-P to select the file, then ctrl-G, enter line numder and press enter. Cmd-down for end, cmd-right for end of line and so forth. Has vim and emacs bindings available as well, and you can easily customize your set to anything you like.
• World completion for same-file / same-project as well, and via extensions for your favourite sets of languages, libraries and frameworks.
• Colors and styles are customizable as well, and not limited to any vt-terminal sets either. There are plenty of themes available, again easily installed and updated via Package Control.
• Has diffing and SCM integration and such for practically every scenario via extensions.
• Integrates nicely with the GUI human interface guidelines on Windows and OS X, and is a very usable Linux app as well.

The only major drawback I can think of is that it costs money (which is pays itself back quickly as an investment, if you edit text professionally), but it's unlimited installations on as many computers you want to run it on as long as it's you using it. The free "trial" version is fully functional except for the registration nag popups.

Personally, I've used both emacs and vim in remote sessions for quick edits for decades, but that hasn't been enough to learn more than the basics of them. Meanwhile, I've done a couple of decades the BBEdit -> TextMate -> Sublime Text route, which has allowed me to transfer the skills to the next editor and focus more on code itself without mental context switches regarding text editing between the editor and the rest of the system. For remote editing, I've been using rmate since textmate, or nano for the random config file and such edits even locally.

So tell me why anyone should invest time in an editor like emacs unless they already have the the decades of legacy of rewiring their brain to work with a single editor specifically? Same goes for vim. Honestly, there are much better, more flexible and extensible editors out there nowadays, like Sublime Text.