That's actually not good at all, it means we are looking at a significantly flattened (as in the curves are not as extreme) Bell curve for Bitcoin global hashrate between 2009 and 2140. I guess this is why people have been saying that more incentives for Bitcoin miners are required to guarantee that the hashrate stays more or less stable once block rewards in BTC denominations start to become scarce.
Nope. I'm assuming a theory whereby circulation remains constant and all the other factors being invariable, which is often not what happens in real life. Bitcoin gets deflationary, fees increases, etc; Satoshi's rationale on reward halving may very well hold true assuming improved efficiency in mining and a compensation in fees. Reward halving doesn't encourage more miners to join, the compensation and the other monetary factors (real cost - reward, etc) are what makes it attractive.
Regardless, discussion about this would be diverging from the issues that is being discussed here. Would be more of an economics question rather than technical.