The problems with MIPS are not technical or ecosystem or being battle-tested or not. The problem is it is proprietary and since sometime between when SGI spun it out (and the expected rise of Itanium) and the purchase by Imagination Technologies it has been run by a series of incompetent and/or people who just want to extract as much money as possible and then get out. They've had some great technical people throughout who have revamped an modernized it, but in the end it's the proprietary nature and mismanagement that has been more important.