I don't disagree in any way Ken, I'm all for the move but I just don't see it happening any time soon. I can't speak for all trusts but certainly in the handful I've worked at, I can't see it happening for a decade at least.
It'll take several more WannaCry type incidents and several more huge security breaches before the people holding the purse strings will register that something needs to be done. They'll then set up a task force to examine what needs to be done, this will run for a minimum of two years. The task force will be made up of a horde of finance and procurement people, staff representatives in the form of union reps (who's job is solely to be difficult, irrational and obstinate) and a lone brow beaten representative from IT. They will then inevitably recommend the path of least resistance which will be Microsoft.