I’ve seen a few references to 2.2KW spindles, but this topic is the only one I’ve found where I can see one mounted. As for “successful,” as with a lot of MPCNC mods, we don’t have in follow-up information about how the build performed.
The Makita RT0700 series routers, common on the Primo, are roughly equivalent in power to what a 1000-watt spindle would output if such a spindle existed. Common spindles are 600 watts, 800 watts, 1.5KW, and 2.2KW. I’ve always thought that a 1.5KW spindle would work well and provide some additional power over the router. I would hesitate to mount a 2.2KW spindle. The significantly higher weight is a lot of mass to be accelerated and decelerated. @stevempotter uses a 1.5KW, water cooled spindle on his machine and seemed happy even before he did his significant upgrades.