Some of the responses missed the part that this is about Unity.

While it has some flaws, Unity's input mapping system is quite capable. (Sometimes it is a bit tiresome, like mapping all XBox buttons for all controllers, but those are free to download).

With only a tiny bit of work you can configure the game to accept input from the keyboard, and from a controller, from a force feedback joystick, from a flight yoke, from alternative UI devices, whatever they want. If they want to remap arrow keys to WASD or IJKL or whatever they can do it. If they want to reverse up/down or left/right for their preferences they can do it. If they want some buttons one controller and alternate buttons for the commands on another controller, they can do it.

Set it up right and it doesn't matter what they use. All that matters to the game is that you have axis values and buttons for input.

If you need keyboard input it is slightly more difficult for non-keyboard configurations, but those are also handled fairly easily. There are plenty of tutorials on making a UI for keyboards that generate key events the same as regular keyboard events and also reading actual keyboards, then you can process them the same way. It gives the user the option to stay with their gamepad to type with their thumbs, or to start typing on their keyboard, or both.

TL;DR: It is Unity. It's easy to support both.

Thank you for the detailed and informative responses, everyone. It's clear to me now that I have to support both Keyboard/Mouse and a game controller (s), at the very least. In addition, all types of input have to be configurable with ability to save input configurations, of course, and an option to reset to defaults.

The next question I have is whether to use a third party input system for Unity, such as ReWired, or Unity's new input system. I have done some research into ReWired and I agree that it is superior to what Unity offers out of the box today. However, there is a new input system in the works for Unity, which sounds promising, and they should be releasing an experimental version this summer. Here is a link to their blog: https://blogs.unity3d.com/2016/04/12/developing-the-new-input-system-together-with-you/. In general, if Unity offers a certain feature out of the box, I prefer to use it over any alternative third party solutions, provided their functionalities are fairly similar. Any opinions on ReWired vs. this new input system?

Reminds me of my wait for the new UI system. It took several years longer than they promised and was in a shabby state out-of-the-box. 2 years on, it's pretty usable, but still with some unnecessary complexity and missing functionality. My advice is not to wait for official features. Use what is there now, migrate if new stuff appears and is better.

Some of the responses missed the part that this is about Unity.

While it has some flaws, Unity's input mapping system is quite capable. (Sometimes it is a bit tiresome, like mapping all XBox buttons for all controllers, but those are free to download).

With only a tiny bit of work you can configure the game to accept input from the keyboard, and from a controller, from a force feedback joystick, from a flight yoke, from alternative UI devices, whatever they want. If they want to remap arrow keys to WASD or IJKL or whatever they can do it. If they want to reverse up/down or left/right for their preferences they can do it. If they want some buttons one controller and alternate buttons for the commands on another controller, they can do it.

Set it up right and it doesn't matter what they use. All that matters to the game is that you have axis values and buttons for input.

If you need keyboard input it is slightly more difficult for non-keyboard configurations, but those are also handled fairly easily. There are plenty of tutorials on making a UI for keyboards that generate key events the same as regular keyboard events and also reading actual keyboards, then you can process them the same way. It gives the user the option to stay with their gamepad to type with their thumbs, or to start typing on their keyboard, or both.

TL;DR: It is Unity. It's easy to support both.

Would suggest using an asset store extension such as incontrol though, as control mapping from controller to controller will vary significantly natively and can be a burden to work with (and though Unity is quite capable, the axis configuration is still a mess to work with tbh).

But the TL;DR is pretty much on point: Why not do both given it shouldn't take you more than half a day to a day depending on the project's scope.

Reminds me of my wait for the new UI system. It took several years longer than they promised and was in a shabby state out-of-the-box. 2 years on, it's pretty usable, but still with some unnecessary complexity and missing functionality. My advice is not to wait for official features. Use what is there now, migrate if new stuff appears and is better.

That's great advice! Plus, if an input system is well designed, it shouldn't be too hard to switch from one system to another, if necessary. Good software design principles are universal, after all. Thanks for that.

@kburkhard84 It's unlikely it'd be finished soon, i.e. it'd probably take a while longer.