I think you are slightly wrong.
I believe that the M.2 interface supports both drives that support SATA and drives that support NVMe. So if matched speed is essential to you then you can do it by using one M.2 SATA drive and one standard SATA interface SATA drive.
As the previous post suggests, you may be confused about which RAID level is which. At least, you need to make clear which RAID level you want.
RAID0 is striping - content is spread across both disks - speed is limited to that of the slowest disk (but in theory you may get twice the throughput of a single disk) - there is no redundancy and the failure of either disk wipes out all content, so the MTBF is lower than for a single disk (but you do backups, right?)
RAID1 is mirroring - content is duplicated across the disks - read speed is (potentially) that of the fastest disk / write speed is that of the slowest disk - there is redundancy and the failure of one disk does not even need to be noticed (but you had better notice it!) and you still need to do backups (you do backups, right?)
(Language chosen to assume two disks, when RAID as a concept can be applied to more than two disks, but realistically you may not get more than two disks in a laptop.)
I don’t know that you are really worse off, in either RAID0 or RAID1, having one NVMe speed disk and one SATA speed disk, as compared with two SATA speed disks.
Pretty obviously you would be better off in either scenario having two NVMe speed disks. Who wouldn’t want that even if not doing RAID at all? Whether there are enough PCIe lanes is another question.
I would guess that RAID0 support would be a can of worms, as it would require support in the boot process - unless the RAID0 is implemented in the firmware but that in itself could be a blob can of worms. (So people may use a non-RAID0 boot partition and LLVM or similar later in the boot process in other partitions.)
I would guess that RAID1 is easier since up until the first write operation the RAID can basically be ignored.