Southwest, which is truly a US trunk carrier now, would do well to try code-share agreements with select smaller carriers, instead of 'going it alone'.
I suspect that they may well try this in the future.
This would conserve their cash position, meanwhile provide added capacity.
However, should they try this, they need to be sure that the smaller code-share partner can provide the same level of service that Southwest is known for...just basic, on-time air transportation.
Anything else will absolutely not do.