I wouldn't say there's an endgame, hash power should continue to grow until the end of time (or bitcoin).

But, doubling in power every month is a short term trend.  There's many factors that play into overall network hash rate, but ultimately the limit will be on the technology available.  These rapid increases we're seeing are because Bitcoin ASICs are still relatively new and their chip technology is quite a ways behind mainstream microprocessor tech.

As ASIC fab process get closer and closer to currently available general purpose processor tech, that growth rate will slow.

In one year we've gone from 110nm process ASICs (chip tech circa 2004) to possibly 28nm process ASICs (chip tech circa 2011).  That's 7 years of chip technology crammed in under 12 months!  Of course we're going to see huge hash rate increases.

If bitcoin prices continue to rise, we'll probably see ASIC die processes just about caught up to mainstream processors at some point next year (newer processes are quite a bit more expensive than "ancient" ones, so the demand created by BTC price has to be there).  From then on, hash power growth will be a function of what's left of Moore's "law", the number of miners buying new hardware, and BTC prices. 

Heck at 28nm, that's already caught up to AMD's chip technology.  The amount of R&D necessary to efficiently and reliably package high performance chips at smaller and smaller nodes goes up quite a lot.  Intel is only on 22nm for their mass-market processors.

We may never see difficulty jumps over 40% again, and if we do they will be few and far between.  So I guess I agree with the OP in difficulty jumps tapering off and I would go so far as to say the peak may have already happened for a one-month timeframe.