After reading through the whole thread, I'm starting to doubt if some of these are unpopular. But I hear so many people say the opposite that I think they are.
-I actually really like Gachapoid. So much that I jokingly will call him "my son". I think at first I didn't like his voice (and sometimes prefer other vocals before considering using him), but it just sort of grew on me. It's quirky and different, but honestly a little cute when done well. Actually I think that's something with vocals, it depends on who uses them. Some producers can make "bad" vocals sound "good" and vice versa. Some producers can make realism or good pronunciation out of vocals. I feel like kyaami made Miku V3 sound amazing in their V3 vs V4 covers.
-Please. Please use lower ranges more often. There's nothing wrong with higher range, but some of the voicebanks have much more potential when you go lower. I just don't like seeing Cyman be tortured when his demos show he sounds better when you go lower. I say lower, but thinking more carefully, maybe mid-range? I guess I hear so many higher range that mid-range sounds lower. Actually a lot of male Vocaloid songs abuse the high range. Amy is another vocal I hope to see used like this. When I first heard her, I just could see her as Delores from Sister Act (probably because I saw it not long before V5 released). I feel like this is more of an unpopular producer opinion rather than fan opinion.
I had some opinions, but reading through the thread kinda shocked me. Do people really like GHOST and anime/moe style more often? I always thought that more Vocaloid fans hated GHOST and were sick of moe appeal characters.
Edit because I forgot one and don't wanna double post: I don't actually mind tuning a Vocaloid to the point where their voice sounds different. I think with the right creativity, it could be done well. Kikuo and mafumafu come to mind when listing examples. But I also don't mind the fanmade genderbents. Maybe that's because I more of see story potential in using it. Tuning a vocal to sound like a different age in different parts of a song/series is something I've only seen done in 1 song.