The problem is they thought those 3rd party ports would be enough to encourage people to buy the system. Same thing happened to 3DS hence why both had/have long game shortages.
For now they need to realise they are the only ones who will support their system so they need to fix that issue first to ensure a constant flow of software before trying to get more 3rd parties onboard (this includes future platforms they release)..
This isn't easy cause working faster will compromise the games and getting more people will only have too many cooks in the kitchens so to speak. The only way I see out of it is if they hire a lot of new smart young talented people who haven't got experience yet and mentor them up and train them. Assign them to each team so they are constantly learning.
Then eventually create a new teams and repeat the cycle with old guys to mentoring a new batch the Nintendo way of developing games. In 3 years time when next gen is ready they should in theory double their team numbers to cope with more projects.
They also need western dev studios that can have the freedom to try and create new ips like naughty dog has for Sony.
