By the time it hits the shelves, next gen consoles by Sony and MS are already released, or close to release. It won't help Nintendo if their next console (whether a Switch pro or not) is not powerful enough.

It will help them fine by late 2019/early 2020. PS5-XB2 only games are likely a ways off, cross-gen was long enough this gen as is, next gen will be even longer because of PS4 Pro + Scorpio, and devs won't want to make those huge budget PS5-XB2 only games and ignore 160+ million install base of the other platforms. 

Then by 2023, Nintendo can release a Switch that is even more powerful than that one just as PS5 cycle starts to ramp up. 

Honestly though, streaming services will likely start to take off around then as 5G adoption grows and then consoles in general could be in trouble. 

NBA had the biggest launch ever since NPD started tracking and didn't even come in the top 10 on Switch this month despite having a perfect tracking period. Many games just aren't selling that well to the userbase and if you have to make an exclusive to make some cash then who gives a shit unless you would expect your (likely lower budget) to fail on PS4/XBO.

I dont see how Pro will help with current Switch hardware on which those games would also need to rum.

Maybe Nintendo will have a solution for that too. They did patent a supplemental computing unit. 

I wanted to post this for some time, but i end up forgetting.

I saw this link that Miyamotoo posted regarding carts for Switch (posted because of price issues? can't say, now): https://www.resetera.com/threads/are-carts-hindering-switch-reach-in-the-same-way-it-did-with-n64.36840/page-5
I think the thread is probably focusing a little too much on cart sizes issues.

If those insiders are to be trusted (have heard about one or two of them for quite some time), there's also another important issue that hasn't been adressed:
A few quotes by NateDrake:

"Power is on the lower end of concerns from third parties. Game cart size capacity is a far bigger issue that needs to be solved for third party support, as are software sale performance."

"32GB carts are available now but are extremely expensive. 64GB carts next yr will help a bit but, again, are expensive. Software sales are a mixed bag."

"I can say it is on the lower end of concern, because cart size and software sales are bigger issues right now. Games have been cancelled for Switch due to the limitations and cost of carts. Other games have been shelved because software sales."

In regards to the OP, sales seem to have not completely pleased 3rd party makers.
If this means western or japanese makers, or both, i didn't see anything that clarifies this, but someone isn't exactly happy.

He also said:

"These aren't my concerns. They are concerns I've heard from developers contacts I have. Numerous projects are not coming to Switch because cart size limitations and cost. Games that can easily run on the platform are being skipped for those reasons".

Just for record, he is only one insider that mentioned "mixed bag" software sales, other were mostly talking about carts size/cost problem.

True.
And i didn't try to say that we should forget about the carts conversation, as if there was something more relevant. I just found that this could - and should - add something to that same conversation.

Sales are a mix bag; caused SW to be cancelled; SW sales performance, are something we shouldn't be overlooking. On the contrary.
Actually, it kinda goes against the idea that everything on Switch is doing awesome.

It's just one insider, as you say. But we don't know what type of games is talking about (ports, remasters, AAA, etc.) or if the other insiders know but for some reason, decided/didn't think about that to the point of commenting on that.

Just saw the NBA 2K19 sales. Absolutely terrible.

PS4 - 775k
XBO - 415k
Switch - 35k

Installbase isn't an excuse when it's now over half the Xbox one.

People buy Switch mostly for Nintendo 1st party and the fact it is a portable too.  Of course most don't care about watered down 3rd party games, that's why selling numbers are 

embarrassingly low on Switch compared to X1 and most of all PS4.   When PS5 and Next XBox will be released, I think you will only see 3rd party puzzle games or mini games coming to Switch.

Nintendo naturally do not care about it, they conceived the console like this, and you cannot have everything.  They made a choice.