Just a theory, since Xiaomi released cepheus this week, but not raphael, and from the fact that building davinci was very difficult for us due to not enough space on system partition, I would say that many of Xiaomi's difficulties with updating older devices are due to the lack of dynamic partitions on these devices, which forces them to make changes like not preoptimizing (preoptimizing results in faster first boot times and saves space on the data partition, not much else) and removing optional apps altogether from their ROMs for older devices, all because they have to fit their ROMs to predefined partition sizes.
Luckily, this doesn't affect us, usually, since we manage to fit our ROMs without issues, but for davinci we had to make an extra cleaning step that freed 75MB, which was enough to complete the build. Hence the delay on our side with releasing davinci. I can only imagine that this could be the reason why raphael wasn't released, since it's ROM is almost the same as cepheus's ROM.