When releasing games on consoles, I vaguely recall that console manufacturers have a requirement that important UI elements need to be away from the edges of the screen, because different TV's can accidentally cut off some of the image.

A) Is this still true with modern TVs? Do console manufacturers still require it?

B) How much space should I give my GUI elements, if I wanted the game to be released on consoles?

C) What constitutes 'important' UI elements? If I have a UI window in my game, and a little of the purely decorative frame of the window gets clipped, is that a problem?

Right now I have a 20px UI padding around the edges of the screen - is that sufficient? (the game's background fills the screen, just not the UI elements)

Thanks in advance!

Most if not all display device have some form of overscan which is why there was the requirement to keep displayable element within a certain tolerance of the display boundaries. With that said I would not hard-code the padding values as it would be easier to just generalize the padding to be a fraction of the display width and height. IIRC 5% overscan should be a pretty good low water mark. Meaning offset display elements by 5% of the width and height of the display respectively. This is the value I've used in my projects and it seems to be good enough so that nothing gets clipped.

3 hours ago, Servant of the Lord said:

A) Is this still true with modern TVs? Do console manufacturers still require it?

Modern TVs and displays can have this turned off, but it varies. 

Each console has different rules.

3 hours ago, Servant of the Lord said:

B) How much space should I give my GUI elements, if I wanted the game to be released on consoles?

Combining all the requirements is about (not exactly) 5% each side for full screen HD displays. It gets more tricky when there are more advanced requirements like XBox Snap areas or for lower screen resolutions.  So about 1720x972 for a full screen 1920x1080.

3 hours ago, Servant of the Lord said:

C) What constitutes 'important' UI elements? If I have a UI window in my game, and a little of the purely decorative frame of the window gets clipped, is that a problem?

Mostly depends on who you get looking at the game and how strict they are feeling.  

There are different sizes of safe zones for different things. Title images, UI elements, and action areas have different "safe zone" margin areas on different platforms.

3 hours ago, Servant of the Lord said:

Right now I have a 20px UI padding around the edges of the screen - is that sufficient?

Nope.

Thanks guys. I'm not hardcoding it per-se.

My game supports split-screen coop, which means I'm trying to figure out what my minimum supported resolution would be, and halfing that, and thinking about padding, trying to figure out how much horizontal space I'd have for menus.

i.e. if the Minimum I support is 1280x720 (720p widescreen monitors/TVs), then half-that in split-screen is 640. So I was mentally subtracting 20 pixels on each side, and thinking about making the menu panels have 600 pixels of usable space.

Doing 5% gives me about 560 pixels wide for split-screen menus worst-case, which is doable, but gets rather cramped.

What is the minimum resolution console games must support on modern consoles? What about non-widescreen TVs?

Can I *assume* a minimum of 1280 width?

Or, I guess I should ask, what assumptions can I make about resolution? That'd help me design the basic design, with the understanding that I'll also need to support different ratios and so on by cropping, scaling, or letting the hardware scale it.

I want to avoid only scaling for different resolutions, or text will get all blurry.

It gets tricky quickly and bumps against NDA territory.

480p is still officially supported plus officially not recommended. The PS4 Remote Play (which is mandatory on PS4) has a lowest resolution setting of 360p, that's 480x360.  I'd expect most games would be unplayable at that low resolution unless you were incredibly familiar with the controls.

Most games these days assume a minimum of 720p displays for UI elements.

It is hopefully enough for planning purposes to assume about 5% on each side, to understand the console may display in standard definition or possibly lower, and to know each console has different requirements.

Thank you, that helps alot. I'll assume 720p or greater (and certainly test well for 4k and 1080p, which I'd guess most people use) and can just scale down the entire screen for resolutions that likely nobody will use.