Well, lets first ignore the sayings that switch dont need them. Lets supose that switch need to get the AAA third party games. Lets also ignore that not building these AAA games on switch is a bad industry practice, and lets consider that nothing we do will convince them to do so. I can only see 3 solutions.

1-Streaming. As long you are connected, you can play the games that are not being running natively on switch, they are on a cloud server. We already have seen some tests with RE7 in japan. 

Suggested way to do it: MS announced on E3 that are building a streaming service for you play your xbox games in any device (phones, PCs), Nintendo and MS should partner (and we have current evidence for their closeness) and bring this streaming service to switch also. MS seems more worried to get subscriptions than in selling hardware per se (we have plenty of evidence), each switch owners would be a potential subscriber. 

The bad: requires constant internet connection. As switch is an on the go system, this might not be avaliable. So, people wont have the access. Price, generally requires subscription or to pay. You lost the legacy of your games as you depend on cloud. 

2- New hardware. One of the factor of developers skip switch is the hardware. Despite the audience may not be there, if the hardware was as easy to port as pressing a button on their UE4 IDE with no constrains, more games would be on switch.

Suggested way to do it: create a new gaming hardware that follows the PS5 or next xbox specs as close as possible, include a switch chip (or at least, put a slot to people plug their switch like a dock) to run switch games too. 

The good: Development process for games, they can market as the next gen home console experience.   

The bad: price, lower initial installed base, install base split, wont be in fact a switch.

3-Create porting teams. If third parties do not develop the games, let Nintendo create studios specialized with AAA porting. Offer to port the games, handling development, publishing and sharing the profits. That could be applied at least for the Key games, like GTAV, MHW, RDR2, KH3. We have seen panic button bring doom, wolfenstein to switch, switch has modern features to handle the new technologies of games like dinamic resolution, but with given restrictions(particles, resolution, geometry, textures), the games can be ported and present a playable version on switch.

Suggested way to do it: Create 2 western and 1 japanese studios, working on the porting process of a minimum of 1 big game a year. 

The bad: They wont have capacity of porting every game, so, the library would still lack. Publishers may deny to get downgraded version of their 'masterpieces'. The compromises can sometimes affect the playability of some games.  

The good: Having key big third party games on switch library.

Any other suggestion of solution not based on streaming, new hardware or creation of porting teams?

Which one is better? (id like to see either 1 or 3)

None of these solutions is worth the effort. I know you don't want to hear it, but the obvious and in my opinion best solution is: Fuck AAA third parties. Nintendo doesn't need them, the Switch doesn't need to seller better than PlayStation, everything is fine and dandy. There is no reason for Nintendo to shell out huge amounts of money when they are perfectly fine with the money made from their own games and indies, who really seem to love the Switch.

Number 2 is out of the question. There is absolutely zero chance that Ninty releases Switch-family hardware that is statistically equivalent to PSbone before those guys move into their next generation.

Number 1...... Streaming does not seem to be ready for prime time just yet. But, in theory, something like this may happen over the next several years.  I'm not holding my breath though.  

Number 3 seems reasonable at first glance. I think it would be something more along the lines of Nintendo buying the code and Switch rights for various games. But, I am not aware of any of the hardware guys ever doing this before. I'd have to bet against it.

I'd like to offer an option number 4 - The Switch install base grows to such a point that third party publishers just cannot skip the system for business reasons.

Switch just needs to continue to sell forcing many of the so called AAA's to cash in or loose out, it's that simple

Solution 4: buy a PS4. Who needs third parties on Switch? Nintendo doesn't want them, fans don't want them, and third parties don't want to be there. People are creating a problem out of nothing.

To complicate it a degree, switch successor has to maintain the same sales force and hardware concept. 

4. create unique games or spinoffs for the Switch instead of trying to port the games for the Switch somewhere down the line when everybody has forgotten about them already.

^

5. Nintendo pays third party devs to port their games.

Right now for the Switch hardware that we currently have, all Nintendo has to focus on is getting Japanese and mid range publishers / developers.

They have always had dicey relationship with EA and other major Western third parties besides UBI Soft, plus logically if the third party wanted to port the majority of their titles to the Switch it is doable short of them building their game exclusively with 4K or some other high end tech in mind. As successful as the Switch is globally there are plenty of ways to support it whether it is with a port or a separate team that works on lower spec games that could be released on it. However with new hardware a year or two away, most won't bother to invest that heavily in learning or adapting to aging tech.

Japan development for better or worse is much more compact and used to tighter budgets, plus globally while not in the same realm as CoD or FIFA they have a strong audience who as we have seen with the Switch and PS4 this generation can be a force to move products.