Before my MacBook Pro died yesterday my iPad was basically a really expensive video player. I'm stuck using it for home computing tasks until I get my laptop repaired and it's not a bad experience. Is the ideal experience, though? No. I see the utility for different people and sectors but as a primary computing device? It'll never be that in it's current iteration.
A larger iPad could be interesting but, keep this in mind, why would they release a 12-inch iPad with a keyboard dock/case/whatever running iOS when it would directly compete and cannibalize the newly released MacBook? There's no reason for both in the line-up. You want an iPad with a keyboard? Get the MacBook. You want a touchscreen device? Get the iPad. There is no reason for Apple to muddle up their lineup with that device.
A larger iPad could be interesting but, keep this in mind, why would they release a 12-inch iPad with a keyboard dock/case/whatever running iOS when it would directly compete and cannibalize the newly released MacBook? There's no reason for both in the line-up. You want an iPad with a keyboard? Get the MacBook. You want a touchscreen device? Get the iPad. There is no reason for Apple to muddle up their lineup with that device.