The trouble with making specific hardware is that there is no guarantee the a device can be jailbroken and can stay jailbroken. You can imagine all the returns a hardware manufacturer would get because people "accidentally" upgraded their device to a non-jailbreakable version of IOS. It could also make support quite tricky.
Hardware generally only becomes cost effective at volume, therefore you would need to shift a lot of units and keep the momentum up for it to be reasonably profitable. Jailbreaking is very popular, but I'm not sure there is a killer peripheral which enough people would buy...
A more typical usage scenario is for jailbreaking to enable the use of hardware which is not supported by the iPad. For example, I use my Apple Magic Trackpad quite nicely thanks to JB bluetooth mouse drivers.
Interested to hear what kind of hardware you are envisaging.
Cheers.