For me the SNES represents an interesting dichotomy.
With regards to NES and my nominal C64/128 development the SNES is relatively as so
NES : stuck is a desert with a small canteen and a walking stick
C64 : travelling through the dessert with a well stocked camel caravan and a compass.
C128 : travelling through the dessert with a well stocked camel caravan, a compass, a large water reserve and a motorbike to scout with.
SNES : living it up in *****s at the Hanging Gardens of Babylon eating grapes and drinking wine with a fan-boy to keep you cool.
we are all suffers of the 6502, the 65816 is a lovely CPU that fixes most of the issues, makes coding less painful, 2.5~3.5 mhz and 16 bits easy... Hardware Mul and Div to make up for the CPUs lack of operations, happy sigh. It has stack relative commands which helps with C. The ability to move the ZP and Stack allow for making micro threaded entity systems.
Then large number of sprites, 4 moveable planes, windows, colour, palettes, dedicated VRAM, dedicated Sound chip with its own RAM. DMA channels out of our ears... HDMA... 8 button joypad... and then we can drown in ROM...
So why do we waste our time with the NES and C64/128 when we can just live it up on the SNES and make the same game we make now but in half the time?
That leads to the other half of the tale...
Because if we did launch the straight C64/NES game on the SNES we would be laughed at. The SNES has all the toys and the disconcerting customer will demand them all. Just in the way a C64 game these days has to do all the tricks or go home, a SNES game will have to be top of the line... a top of the line SNES game is 5 people and 2 years of work.To which if I'm going to put in that work I might as well use game maker, get it done in 1 year and sell if somewhere I have a hope of making money ( a hope, not a reality ) like Steam. Because there aren't really any publishers for the SNES, you even still call the NES "homebrew", ( do you have NES publishers? )
Lets make a SNES game, is it a platformer, is it as good a SMW? DKC? ok no lets make a shooter, R-type3 Daruis good? JRPGs the SNES was king of those, is Chrono Trigger good, Terranigma, FF6 good? the bar is very high.
However this is 2017 and we have lots of new toys to get the development time down... only the SNES doesn't seem to... I first go into SNES dev on my P133 when Y0shi's doc was the only doc, and it seems if I wanted to do dev now my best bet would be to fire up the P133 and use the tools I had back then, as they won't run on my modern machine and there doesn't seem to be much to replace them...
I don't think fixing the lack of C compiler is going to really move the needle. Sure they modern people can say... oh man asm... but I want C.... but then if you give them C it will be... wait palettes you mean I can't just draw a png in photoshop, I have to work out tiles, I can only play 8 notes and not an mp3... the game maker crowd will never really push through the hard work of doing SNES dev, C or not. For me, C would be good enough on the SNES for doing presentation and general flow, but I would imagine I would need to kill the C runtime and drop into a pure ASM game core. It would save some time but not a lot of time. For me the rest of the tools,docs,turn key solutions would help a lot more. Porting the MACROSS assembler to 65816 might make a gentle halfway house though.
I don't think having C is the only push for getting more MD games, the fact it shares its core with the Amiga and ST means all their tools can be ported and the MD was more popular in the Euro zone where the demo coders are. They will just bash out a MD game for the fun it and to do something different for a change. Nintendo dominates in the US which doesn't really have a demo scene or programming mindset when it comes to computers. Also the MD has a lower standards.
For me the first step would be getting the tools and getting c# libs up to snuff, so people can make content, and build custom game tools quickly.
Then get some off the shelf solutions for things. The Audio tracker + playback code, standard joypad reading code, basic sprite bolting animation and movement system, something like http://codebase64.org/doku.php?id=base:start
maybe port exominizer and make custom versions for it to depack to VRAM etc