rGcxmspVVftpiqLUzTVXLB7752fxLP8Xic

There's nothing to stop them from doing that but why would they want to?  They'll basically be giving away money to the common man (something banks aren't willing to do today in the form of loans).  After acquire most of it, the remaining coins would be mostly worthless, as others will just move on to another crypto currency and there would be little demand for Bitcoins.

Realistically, it'll be much easier and cheaper to destroy Bitcoins via other means than buying it all up.

If any of the encryption used is broken or greatly weakened, they will have start the process.

You may be right in that they won't change it due to ASIC being much more efficient than GPU, as they didn't do it when GPU took over CPU.  However, CPUs and GPUs are general purpose, commodity products while ASICs are for a specific purpose that only a few would purchase.  Everyone else would become marginal and try to have changes made.

You'd need to get in early to make decent returns.  The longer you wait, the harder it will be to make money.  Add into that the possibility that the developers might change how hashing algorithm so that ASIC won't have a huge advantage that it's enjoying now and you might end up losing money.

If you're looking for something that'll be fun, get a GPU and you can do lots of fun things with it, but you won't make a profit.  ASIC is only an investment and there's really nothing else you'd be able to do with it unless you enjoy looking at numbers update.

10 minutes is just the target time to solve a block.  As others have stated, it readjusts every 2016 blocks.

As ASICs gain dominance, there will probably be an effort to change how the blocks are hashed so that CPU/GPU miners will be able to participate again.  A controlled forking will be necessary to make the switch without causing major disruptions to the network.  This would have to be done by having the new hashing method be verifiable by older clients and then having the old and new hashing methods both running until enough miners are using the new clients.  Once that happens, the new hashing method will become a requirement and the old hashing method would be ignored by the majority of the network; those that are using old clients will be forked to an unofficial chain.

Have you tried underclocking the GPU to see if there's a problem with it?