The most important things Nintendo needs to get right for the Switch 2 are 1. actually making it a Switch 2, and 1. ensuring that the system has a steady supply of games ready throughout the first year.
The 2 things that most doomed the Wii U were reinventing the wheel again for no reason with the gamepad, and the wasteland that was the post-launch period. The console died because the 6 months after the launch it barely had any games coming out because Nintendo was struggling with the switch to HD development. Even though it was woefully underpowered compared to the PS4 and XB1, it almost certainly would have been better off waiting a year and launching with Super Mario 3D World, Pikmin 3, and Wind Waker HD and then having a steady stream of great games like DKTF and MK 8 in the first months of 2014. This is the same problem the N64 had and why that system lost all momentum after selling really well at launch and immediately after.
The Switch maintained its momentum because it had a steady stream of releases. Mario Kart 8 Deluxe was not a launch title even though it could have been, instead coming out slightly after launch. This was brilliant and led to the continuous releases like Splatoon 2, Mario+ Rabids, Odessey, and Xenoblade 2 from summer through winter. It never had those months-long periods where nothing was coming out that the Wii U had during the first half of 2013.
If the games are not ready for a steady supply of new releases throughout the first 6 months of the system's life, then they have to wait until the games are ready even if the hardware is ready to go.