I'm cautiously optimistic. I think it's a good long-term move for Nintendo's business, but it's one thing to have a good idea, and it's another execute it well.
If Nintendo do execute this well, then their NX platform benefits from greater development resources and ease of development (due to more cross platform titles and shared tools/architecture), ensuring a steadier stream of Nintendo software which retains its high quality. Before this, Nintendo launch high-profile, commercially and critically successful smartphone games, which expands their audience. Nintendo's network orientated platform ensures greater long-term audience retention; "Nintendo" is the platform, not the box you play on. Quality of Life is also successful along side this, providing Nintendo with more revenue and profit.
If Nintendo don't execute well, then one or more of these ideas could fail. Crucially, though, Nintendo are setting up several long-term revenue generators: software on smart-devices, the dedicated gaming business, amiibo and quality of life.
I hope both this partnership with DeNA and NX are successful. Ultimately that would mean Nintendo retains control of their own platform while being more financially successful, which will ensure Nintendo are around for the long-term.