I don't see Linux overtaking either OSX or Windows any time soon, do you?
Depending on the area you are looking at, it already has (in HPC, for example, linux is so far past the post, barely anybody else gets a look in. Just check out the top 500 by OS).
However, you simply cannot compare linux v windows/osx, each of which has literally many millions of home and business users with this situation. You are talking several orders of magnitude fewer users on amiga for a start, let alone "next gen" amiga systems.
If OS4/MOS moved to x86, they'd be up against all the challenges that AROS has faced during it's development. Only by then, AROS itself will likely have overcome some of them.
So, who in their right mind would pay for an x86 version of OS4/MOS when they could get a free OS (which would by then be the more capable system on the target hardware)? Nobody but the most die-hard users in each camp, which probably runs into dozens each.