Thank you Everynone, you have been most helpful!
The 9-slice widget border I feel, is exactly what I need. I did not think of widgets as a possible solution as I’m not used to such fancy UI tools, and I am ignorant of many of the features of UE. This will make things easier than expected, especially the corner scaling.
I was thinking of simply drawing a texture to screen and scaling it by how you mentioned–mesh screen size–up/down to a certain size. Naturally, distance will also cause scaling to occur through a perspective view. The brackets will be clamped to a certain minimum(very small objects)/maximum(very large objects) size, and perhaps the brackets will scale for tiny objects, but retain their thickness. Deusex and Neocron are two examples of bracketing systems I like most, so I’ll spend some more time studying them and how best to emulate their function.
Thanks for all the help!