Don't know if this showed up in the thread already, but I thought it was kind of interesting.
https://twitter.com/NWPlayer123/status/1017608037282926592
Basically, Smash has been in development for so long that it was actually the second Switch game in development!
I went through and pulled some of the serials for the notable games, and here are my thoughts (we're all concerned about game development times, so this might be interesting).
BOTW: AAA
SmashU: AAB
Odyssey: AAC
...
There are no more AA games, so moving to AB. This has MK8D (ABP), ARMS (ABQ), Splatoon 2 (AB6) and 1-2-Switch (ACC). There is a massive gap, going to C, which has Mario + Rabbids (C2G). Then we have D, which has lots: Xenoblade 2 (DEN), Pokemon Lets Go (DW2/DW3), Fire Emblem Warriors (DXH), Mario Party (DFJ) and, surprisingly, Labo (DFU/DFV). E has Snipperclips (EXY). DKC is in F (FWT). Kirby is in H (H26). And Captain Toad sits in J (JH9).
The 'A' games all have one commonality, aside from Smash: being first-party totally developed by Nintendo EAD, which suggests they were planned as early Switch titles from the beginning of the console's conceptualization (especially for ARMS and 1-2 Switch which are designed to use the console's mechanics). Mario + Rabbids is really surprising, but that was talked about in leaks for forever before launch so it makes sense. We know Xenoblade 2 started development in 2014, so I'm assuming that being developed by an external studio (Monolith vs Nintendo EAD) is why it wasn't listed earlier, as it cooked for almost as long as BOTW! PLG couldn't have been in development any earlier than 2016 as the mobile game launched in 2016, so the commonality between the 'D' games has to be external developers (Monolith, Koei and ND Cube; I have no idea how Labo fits into this).
Knowing this now, from a development angle, any of the EAD-developed games could stand a decent chance of representation in the game, even ARMS which a lot of people are on the fence with (ARMS was actually the main reason for making this post). If 1-2-Switch, a game that literally only makes sense with the Switch being totally finalized, was developed after ARMS started its own development, ARMS should have been in development longer than most of us thought.