You could almost say that Japanese support for Sony consoles will fall off a cliff?

Not... really?

i mean if you are going to reduce this to 'things change' then what is the argument being made? Things change all the time, that's life. Just as easily as 3rd party support for Sony could dry up, so could the quality of Nintendo's first party drop to being abysmal. My plans for Friday night could potentially change multiple times before then.

What we can talk about, though, is what the current situation can tell us about trends going forward. Right now, there are various factors as to why Sony won't just randomly lose Japan to Nintendo.

Firstly, this talking point was brought up when Sony dropped the handheld market, and nothing has come of it. It was brought up again when Sony implemented censorship rulings, and again nothing has come of it. 

As of now, PS4 sales are trending above the PS3 (and Sony didn't lose Japanese 3rd party support from that gen to this), while Switch is trending below the 3DS (and well above the WiiU), and they have lost their grip on strong IPs like Dragon Quest and Monster Hunter. 

Sony has stronger and more varied infrastructure in Asia, Africa and the Middle East. These are markets that are receptive to gaming software, and particularly in Asia has shown to help offset the drop off of sales in Japan in some cases. Japanese publishers want to make money, and as long as Sony has the widest reach of the 3 console manufacturers, they aren't just going to not support Sony because Sony is not Japan-facing.

As you said they are following the money, and it is ridiculous to think that the money is only with Switch. It clearly is also with Sony if strong sales from bigger publishers like Capcom to smaller entities like Falcom, are to be concerned. 

Lastly, the Japanese audience is hardly concentrated only on Japanese software. 

The growing interest in e-sports and Western software is already evidence that the Japanese audience can expand their tastes beyond Japanese games. This is the current and potentially future climate we are seeing in the region. Nintendo is not currently positioned to bring the latest of Western games to the Japanese market on a large scale. Sony is, and will easily be the de facto place for these sort of games, besides PC, in the foreseeable future.

More like a gradual downward slope. 

Generally when people try to exaggerate/change the argument I am making it shows they are afraid I have a valid point.

This is one these posts that shows that you aren't really paying attention.  I now see why you are disagreeing with me.  Here are some things you need to know before we continue this discussion.

1) In Japan PS4 sales are neck-and-neck with PS3 sales.  The PS4 is far more successful worldwide, but can't make a dent in Japan.  Sony is losing Japan.  They've also ceded the handheld market which means they've lost even more influence in Japan.
http://www.vgchartz.com/article/441188/ps4-vs-ps3-in-japanvgchartz-gap-chartsseptember-2019/

2) The Switch has been tracking far ahead of the 3DS worldwide.  In Japan Switch is tracking behind the 3DS, but it is rapidly gaining ground.  3DS cut it's price during the first year, which makes it front loaded.  Switch has not yet cut it's price and is gaining ground.  It's going to outsell the 3DS in Japan as well as worldwide.
http://www.vgchartz.com/article/441000/switch-vs-3dsvgchartz-gap-chartsseptember-2019/

3) The Japanese audience is, in fact, concentrated on Japanese software.  The only Western title that they really like is Minecraft.  That is the only Western title where it's popularity in Japan is comparable to its popularity in the West.  Maybe you are thinking that Call of Duty topped the charts there for 1 week?  That is not terribly great compared to how CoD does everywhere else.  The latest chart has it at 4th place in it's second week.  Again, very pathetic by CoD standards.  Most likely CoD will not be in the top 10 for annual sales in Japan.  Every other Western title will do worse (except Minecraft).  What the Japanese buy is 95%+ Japanese software.

4) Most importantly, actions have consequences.  Life is not a random unpredictable mess.  Sony can't alienate Japan and be friendly to Japan at the same time.  They cannot have their cake and eat it too.  Perhaps you think ending their handheld line will have no effect?  It will.  Give it time.  They just stopped making the Vita this year.  Wait a couple of years and you will see an effect.

In the 80's Nintendo had very strict policies for 3rd party companies.  They did this both to rebuild the gaming market and also to maintain dominance.  It seemed like a great strategy at the time and it made the NES the most dominant console in history.  However, their actions had consequences.  They gradually lost influence to 3rd parties, first to Sega, and then to Sony to a much greater extent.  And even to this day Nintendo has a reputation of being unfriendly to 3rd party companies.  Their actions had long standing consequences.  

Sony is now trying a similar thing.  They see that there are much greater profits to be had in the West, so they are turning their back on Japan.  This will have long standing consequences.  First they alienate the Japanese customers and consequently they alienate the Japanese devs.  Actions have consequences.  If Sony stops caring about Japan, then Japan will stop caring about Sony.  That includes developers too.