So Fusion (and all the other competitors) are virtualization platforms, not emulation platforms. That means that they pass through the CPU hardware to the guest. If Apple were to go exclusively to ARM (which I seriously doubt), it'd be a major effort to provide a platform that could still run windows.
If Apple actually does this, I suspect we're going to see both ARM and Intel based macs for exactly this reason - there is a substantial portion of Mac users who require Intel. On top of that, it's a huge burden on software developers to build and test for two different CPU platforms.
Keep in mind that a) this is a rumor, and b) that Bloomberg has been peddling this particular rumor for years without it coming to pass. By the time you have to worry about it, any hardware or software you buy this year will be obsolete.
