it'll be boring and people might quit the game.
Making fully automatic farms and completely automating your skyblock island to your comfort is actually the main purpose / unwritten goal of most other skyblocks I played. You have to understand that, once your challenges are finished, why on earth would you continue farming your carrots and melons? The automatic farm-building is usually a mid to late game thing that actually expands the skyblock gameplay instead of decreasing it like you say.
You already can build an automatic Cactus farm
Aaand, that's actually the only crop you can automatically farm as of right now, and that's just because of a mincraft quirk, not because Cubecraft actively allowed that or something.
Some of the most used automatic farms on skyblock will not work on cubecraft anyways because of the custom timers. Players would therefore have to create different and more ingenious farms to fully automate their island, which is pretty fun imo. I think redstone isn't available right now because they wanted to test out if their servers could hold the relative big amount of data, redstone obviously would've added a lot more. I haven't experienced much serverlag or server issues at all which leads me to believe that their servers are doing fine. I'd love to see some basic redstone tools (Redstone dust, Repeaters and Droppers to start with for example). Adding a block on server lag machines shouldn't be impossible either by setting a tick limit. In short, yes, I'd like to see redstone.