I'm a bit reluctant to assume we'll get that much from 10.0 after blizzard dropped the "no more customization for the rest of shadowlands" announcement. I hope you're right though. I'd love to see
every race get a lot more options.
I don't think it will be a "surprise" (we all kind fo expect it) so much as blizzard now realizes how popular customization is and they can bill it as feature for the next expansion. I want to believe they will go bigger with their focus on customization in 10.0 since they now know that it will garner positive feedback, but it's hard to trust after that previous blizzconline announcement.
I am expecting some amount of customization added, particularly for the allied races, though less so for void elves since they did get some customization in shadowlands whereas most other allied races got fewer or in some cases none at all. That's not to say I don't think void elves will get anything, but rather I think they will get a bit less than the others. I'm just keeping my fingers crossed for black hair at the very least, though I'd like to see a few other natural hair colors added (yes, including blonde) so this whole pro vs anti high elf thing can finally be laid to rest.
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I'd love to see such options added.
MyWholeLifeIsThunder made this mockup of void elf hair in a few natural tones but with void tinting at the ends:
I thought it was well done. He also did this one which is very pretty: