Makes perfect sense
I've been involved in Windows, storage, etc for many, many years now, but of late have been getting more involved in AWS, Linux and agile workloads. If the NHS can embrace these concepts and move to an open source platform it would be of huge benefit. There are plenty of Linux skills around and there's simply no need to have ancient PC's running Windows XP. Yes some applications will need to be migrated/redeveloped, but gone are the days where an application should be tied to an operating system.
As for proprietary hardware, which there will be loads of in the NHS, suppliers will simply have to decide whether or not they want their contracts renewed. Once the messages gets through that Linux will be the new platform they will all follow suit or be replaced by competitors who will. And where there are no competitors, yes some money will need to be spent.
I'm not underestimating the size of the task here, or trivialising how important application availability is, but this culture of pockets of IT that exist within our public services, not just the NHS, has to change. Nor am I underestimating the costs - it will be damn expensive to make the move - but the long-term benefits will be worth it.