The 'problem' with Kyoani is that they make awesome looking shows, yet they don't cater to MANY people's taste. It's only natural that there would be tons of complaints.
But anyway, the complaints are not reasonable in my view either, because it's discriminating against a genre. I haven't ever seen anyone complain about ufotable only doing Type-Moon chuuni stuff since 2008, and I suspect that's because the genre KnK and F/Z fall in is much more respected in the western world than iyashikei slow-paced SoLs. Likewise, I haven't seen anyone ever complain about Ghibli using the same character designs over and over in their works, but Horiguchi (and even unrelated designers like Nishiya and Ikeda) get lots of shit because "Kyoani always rehashes their designs!", something that is not even entirely true to begin with.
But that being said, I too would also like Kyoani to branch out. I enjoy practically everything they make, for the visual presentation if not anything else. But that's exactly the reason I would like them to do more settings, because I love the way they make their anime.
I'd really like if Yamada did a high fantasy anime full of green meadows and exotic creatures, like this:
I'd like to see Takemoto directing a drama set at college, with older characters and broader conflicts.
I'd love for Ishihara to do something totally bananas, like this:
I'd love for them to make a steampunk anime, with lots of awesome plane/ship designs and other vaporous things. Or maybe a cyberpunk "grimdark" show even, featuring gargantuan futuristic cities, lasers, and gore.
How about a space opera? A return to mecha shows? Something like their LN Coppelia, which IIRC is set in a mansion and features a rich boy and two doll-maids alla Rozen Maiden. They could also adapt Kyoukai no Kanata, which by the PV and summaries seems like a sekai-kei show full of action and, albeit set in a highschool, would be really nice to see.
I don't really have any gripe with Kyoani, and I enjoy what they do. Hyouka is my personal AOTY, and I'm thoroughly enjoying Chuunibyou as well. But don't tell me that them branching out and handling any of those settings with the technical expertise they're known for wouldn't be (probably) glorious.