If you have 100M I'll create a company to setup and maintain infrastructure. Though depending on your size I might need more money to maintain yours. Setting up the company isn't hard.

What is hard is doing it today. It will take a year just to figure out the various custom configurations you need to get a majority of users switched over without issue, and there will be a long tail weird cases that will go on for years before everything is done. This isn't unusual - the simpler case of switching my college campus from Coke to Pepsi took over a month and there both vendors cooperated in making it a smooth switch (Coke does not want to burn bridges as this happens all the time and they want to be back again next time the contract comes up - right now Microsoft doesn't have that incentive)