If you want to talk recent history, the N3DS was a spec bump and had an exclusive title. And it was still compatible with all prior software
I don't think any of it matters compared to the future.
Nintendo's new management is very clearly much more focused on profit, they are even doing things like Dragiula (the smartphone app) which clearly go against what Iwata was talking about even just three years ago. They are making a lot of money off Fire Emblem too using the same monetization policies they just a few years ago said they would never do. They are doing paid online. They are loading up on paid DLCs.
$$$$$$ talks. I think what Nintendo learned from the Wii U/3DS era is they need to stop being stubborn and simply get on that money train.
Multiple hardware lines make companies money, even the DSi I think is not really the full extent of what they are looking at, I think the plan probably always has been an Apple like line of products.