The much bigger success of the Wii (1) didn´t translate into full third party games coming to the system.
Don´t expect it now when the power gap could grow even bigger with the PS5 in 2 years.

(1) Yes. Despite that "fastest console sale in 10 months" PR, I believe the Wii had a bigger impact on the market.

Not sure it can handle some of these games to be honest.

First, that's why i said partially. Activision sold from ok to good on Wii, their Wii U games mostly flopped though and they haven't been all to successful on handhelds for quite some time.

At the same time some games just aren't that easy to port. I really think Bethesda did a good job with Skyrim and Doom. Other titles might be harder to port though. And yes, those ports take time.

At the same time we can be pretty sure that most of the big publishers didn't put much trust in Switch, if any. We might see more multiplat games within the next months. Some of them will be older titles. And at least some, more likely many games will never be ported to Switch.

I'm not sure if that's to bad though. With good japanese support, indie games, maybe some western exclusives and yes, even smartphone ports we might actually see a Switch library that is rich yet different from what 'everyone else' does.

Because the system is weak, making the porting process hard.
Because the Switch is still in its first year on the market.

Wait. Seriously. Nintendo consoles usually have garbage 3rd party support in the beginning. They usually build up by the end of the 2nd year. I remember not really wanting any games on the wii 3rd party wise but when 2009 came there were too many to count. The same thing happened with the 3DS and the DS. Wii U was the opposite though. However that is a unique circumstance.

2019 will be when the 3rd party games come in full force. I recommend you clear your backlogs for 2019. Otherwise you will be playing Switch games well into the 10th generation.

Edit: I also want to say that a lot of developers thought the Switch would be another Wii U. So they are now scrambling to get their games on the system.

It definitely takes time to port games over. I think this delay factor is going to surprise people on both Third Party support and the Switch's performance as a console. For 2018 I expect most Third Party games to be ports, mostly old games ported over, but a few games with simultaneous releases on all consoles like Dark Souls. For 2019, I expect lots of simultaneous releases and even a notable number of Switch exclusives from Third Parties. Then in 2010+ the number of Third Party of exclusives is going to grow and grow.

The Switch is currently a large snowball rolling down hill. In a few years it will be an avalanche of great games.

What new "big" 3rd party games have been announced post 2017E3 and summer? i.e. what games are very early in development cycle post Switch launch that have any realistic feasibility of including planning and funding for Switch port in their projects?

I've been saying this for a long time now, Nintendo builds their console with their 1st party games in mind, 3rd parties is like a distant after thought.

Exactly, I am really not sure what games are even coming out that has been officially announced.

Besides the indies,there was a bunch of japanese devs expressing success on Switch. Bandai, Koey, Capcom, NIS, Square, already gave multiple reports about how their Switch releases selling above expectations and how they will improve their support on the platform. From other devs I can remember Ubisoft also expressing good sales, but to be fair besides Mario + Rabbids their other releases were old ports and party games,so the expectations maybe weren't that high.

OP: like many others already said,most of thirds were not on board with the Switch at launch because of the Wii U third party disaster. A big game takes a lot of time to port and again,many of the powerhorse games will not end on Switch. That said,we had a few great surprises with thirds last year and I think we will have more this year.