And graphics cards are messy. Many of them are frankly a lot like accessing main memory without an MMU. It's extremely easy to get scrapes of other application's video RAM that hasn't been zeroed.
I'm not trying to tell you you shouldn't do it of course. Just... be aware. "hijack the GPU" doesn't even require a whole lot of malice. I've had video memory of my firefox tabs from last shutdown draped across my screen while the lightdm login windows do their first paint, for example. This is just the world we live in :(
No worries, I did not undertand it that way. I like it if users try to keep the awareness about potential security problems up.