I would suggest not 'demanding' anything. Linux users are, unfortunately, a
very small percentage of users. I'm one of them, but if Kobo supports Windows and Mac they probably have support for at least 98% of their users in general and 99.5% or more of their users who would need the Kobo desktop client anyway. I'd argue that the desktop client is superfluous anyway; my wife, who will probably never even consider "not Windows", has had no need of it for her Glo; everything she needed for setup (whether she wanted to fake registration or not, which she didn't) she could do without it. Sync books? Wireless. Firmware upgrade? Wireless. Recommendations? Pulled down over wireless with every sync. Books from non-Kobo sources? Calibre, and the Kobo desktop client doesn't allow it anyway. Reading books? Kinda the point if the device
If you really want a Linux client, then you'd be much better to ask people to write to Kobo (snail mail, with real paper and ink and envelopes and everything) politely requesting Linux support. Maybe explain the benefits to all users (never just for your benefit) that would make it worth their time to spend developing a Linux client, and possibly also spending money on hiring a couple Linux developers.
And maybe you could explain to me why a Linux desktop client would be helpful, because I honestly don't see any reason to have the desktop client at all unless you don't have a wireless network. But if that is the only reason, why not spend the time to improve the device user interface and improve the experience for all users instead?