Mat says that he designed the accessory answering readers' feedback on sliding keyboards.
The slide-out keyboard has generated the most response from any of my suggested features. The general consensus stands firm on two opposing viewpoints:
1. Most people would prefer to have an optional slide-out keyboard,
2. but don't believe Apple will ever "go backwards" and release anything like this.
In response to one comment (Mike) I have created what might be an answer to a third-party product which could solve this dilemma.
Actually, not a bad idea at all. It would be even cooler if, instead of being a third-party accessory, Apple actually released a modular iPhone, one that could admit different accessories like these but without the added bulk of building them around the original design. [Planetmat—Thanks Mat]