However, R4.1 now requires a functioning IOMMU to install.
Not quite true, the hard dependency was removed somewhere in the alpha iterations, you can proceed without IOMMU (the installer just show a warning)
However, sys-net / sys-usb will fail to launch as HVM without IOMMU, and if you try to change to PV, it will also fail to launch, because you need to explicitly enable this kernel flag: qubes.enable_insecure_pv_passthrough (commit)
So besides the less security of PV, for system without IOMMU at least they can enjoy other Qubes features.