I think it would be better to see up to the end of 2017 / beginning of 2018: E3 could still be too soon for some projects to be showed off. 9 months-to-1 year sounds like a better wait window to see how the console sells, how some third party titles are received, how third parties will respond, etc.etc.
Going more on detail about this.
The system has been out for not even a month, and E3 happens in June. This means that there is a shorter time between launch to the next biggest gaming fair for third parties to judge how the platform is shaping up, compared to consoles that see their launch during end-year Holidays. Thus, it decreases the chances to see a big amount of third party announcements already at E3. Not that it's impossible: there can be projects that some third parties have been planning while waiting to see more sales datas to see if they should go through with them, and among them there can be stuff ready to be shown at E3, but I doubt there are a lot of them in such an advanced state.
Moreover, there can be third parties who are going to wait a few more months before deciding to put their efforts on Switch with small hesitation: what happened with Wii U certainly made them more cautious, so it's understandable if among them there are people who think that the first month / three months aren't enough to be sure about the platform's perspective. Also, even in the case hardware and software sales are great, I wouldn't start expecting all the major Western AAA "core" franchises to come to the platform: I feel there will still be some brands missing for several reasons (sales potential, possible technical focus on other platforms, etc. ).
Still: if the sales keep staying at good levels, and if the platforms shows to be a healthy environment overall, games will come. It's reasonable to expect a bigger effort from Japanese developers than Western ones due to the platform itself and the better relationships with the former than the latter, but I don't believe Western ones won't act at all if the environment is healthy. Also, Switch has major advantages compared to Wii in terms of hardware capabilities compared to the other platforms: those seriously limited the chances of several games coming to the platform, alongside different-nature obstacles in both the Western and the Japanese markets, but that's another story.
So, yeah, I'll say that, by E3, we won't have a clear picture about the support, while by the end of the year / beginning of 2017, we can start making more accurate / deeper considerations about the state of third party support, mainly from major developers. The wait can be frustrating (I know, I feel a bit of frustration as well in not knowing details about games like Steep, I can understand EDarkness in this), but it's the most reasonable approach to have for now. Again: if sales are good and the software environment is healthy, things will change positively. There are high chances both Lego City Undercover and Puyo Puyo Tetris will be the first two retail, multi-platform games showing how the Switch's userbase is open to non-Nintendo games, speaking of the titles coming in April.