All you have there is a concept drawing. Whilst I get the fact you want to protect your concept, it is a little bit too premature to talk about Patent Pending. What you really mean is that you are thinking that you should patent it. I suggest there is plenty of prior art to make it impossible to get a patent.
A two-bolt handlebar clamp is going to get you into trouble. You need the redundancy of four bolts there.
The single bolt in the telescopic section leaves you with a squirming joint (dynamic joint) in the stem extension section. This will do two things:
1) Drive the owner mad with its creaking.
2) Seize.
You need to drain/prevent water from entering the telescopic section.
No need to go and have a materials discussion. Your material will have to be aluminium. You have no choice.
The design negates 1/2 of your market and that is riders who, for whatever reason, temporarily want a very short stem. The design doesn't allow that, only extensions in the 90 - 120mm region, I'd guess.
You still have not demonstrated an adequate swivel fixture.