I skimmed through and saw something about GUI downloading.
A year or two back, I had a fully functioning GUI download system that got zero attention. I haven't read through this thread too thoroughly, but I thought I'd drop this anyway.
All the code is still archived on GitHub, so feel free to take a look at it and take what you'd like, the project is long gone.
All of the security has been checked over and tested by me and a few other people working on the project at the time (Nullable/DC4F and Greek2Me (a little) if I recall correctly) and it was looked at by some other people. The system was pretty fleshed out and didn't need a TON of work to make normal GUIs work and function, but in hindsight it probably could've been stream-lined a bit.. It also had support for implementing HUD elements, but I didn't do enough experimenting and implementation of them to declare them fully functional.
I don't quite recall where I left the project off, but looking through the GitHub repo, I have a "BLG2" branch that had a few release candidates but doesn't appear to have ever released. I'm not sure if much changed between
that branch and the one I linked to above.
Best of luck.