Something interesting to contemplate but an awful lot of work, even for other games but more on that later.
Others reading.
Images have aspect ratios, it is the ratio of width to height. There are all sorts out in the world (it get quite tedious actually) but the big two in consumer screens and TVs are 4:3 and 16:9, 16:9 being the thing traditionally referred to as widescreen. Let us not even get into pixel aspect ratio.
widescreen is wider than 4:3 (funny that) so if you only have a 4:3 TV you have a few choices as to what to do if you want to sort of maintain the image, distorting it to fit is an option but not one people would take as the differences are too big.
1) Use longest length and cram it into the screen. As you don't want a distort if you can help it then stick big blank sections (typically black bars but I have seen grey bars out in the world, emulator skins often are designed around this, also people that shoot vertical videos often do a nice blurred effect but again I am going off topic).
2) Crop the image down. Fill the vertical and let the images spill over the sides and not be seen. You have two main approaches. A fixed crop, or an intelligent crop that tries to follow the action. You may have heard the related letterboxing before, this is that, generally it is considered a bad thing to do as you then have to redo the work someone else probably deliberately framed. Games, typically being input based in nature, have a further option and the controls can try to direct this. You might have seen it in some handheld emulators which have different aspect ratios and resolutions for the screen than the system they are emulating. The megadrive emulators on the DS did OK here. Your TV should be able to do a basic crop of the image though.
3) Typically seen when converting 4:3 to widescreen you stretch the image according to a pattern, for most this means the middle of the image is relatively normal and the edge gets more and more stretched. For a lot of things this sort of works, at least until someone is on the edge of the frame or they approach the screen to hug it and it ends up looking like stretch armstrong.
Anyway hacking time.
Two approaches
3d games. 3d (and smash is - the thing where you can pause and pan around being evidence of this even if you only ever view from one angle in normal gameplay) is often easier by virtue of most 3d systems using something called viewport rendering, or you don't have to render the whole model of the world you are in, just the line in front of the player (and even then you can do further things like backface culling). If you have ever seen a widescreen hack for a platform then basically that but in reverse and you deliberately render a smaller section, bonus is you don't encounter a lot of the same problems (you are going to less image and not more), or if you do then it is more easily solved (move location of OSD is not so bad).
2d games, this includes most emulators though I would not be surprised to see something using actual 3d for the N64 (the N64 was not terribly like the modern approach for 3d so it is often tempting to go software only). Where the world is there in 3d and you just have to change the behaviour of the camera a bit then it is probably not there in 2d and you have a lot of troubles. Many things will use offscreen as a logic thing (move the thing off screen and it disables the AI. Equally if the logic is something is positioned offscreen and it then goes into the screen and does things then the -10,0 of the original location is possibly in the screen now if you are making a widescreen hack and everything falls apart)
Smash brothers is an odd case as it deliberately uses off screen as a gameplay mechanic. To that end you are going to change how the game is played if you do this, or have to suffer some odd things when it comes to people getting back on the platform. You might be able to negate this a bit by forcing a further zoom out by default and limiting the zoom in more. With that said there is no reason why you could not alter the game to work for a 4:3 world, you might have a few edge cases in level design and the actual process could have a bunch of gotchas but fundamentally you are altering a game within the systems it already has and not even adding much in the way of extra logic into the game; the game does not really care if the screen border is one location or another, indeed it changes it throughout in some cases anyway.
That said this is all on you; widescreen hacks are of interest and benefit to many, hardly anybody is limited to 4:3 and it is not like you are getting back to how it was in an original game in the case of a (bad) remake, or an original style in the case of sequels, or a style of the game that was traditionally and usefully bound to 4:3. In all likelihood this is a lot of work as well, maybe you get lucky and it is just a few values that need twiddling.
That said if you are going to do a vertical widescreen hack (probably not as you said it was too small and this would be exactly the same, unless you also did the zoom thing at the same time) and fill in some info on top of an below then I would be curious to see the end results. Probably not amazing but still something I have not seen before.
The SNES VC filters you speak of are not like PC filters and called at a system level but rather baked in from the ground up.
Also does the wii u not come with its own screen? If you are going to tell me it does not work for this scenario then fair enough really.
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Xdqwerty:
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Sicklyboy:
