I agree with Abnegation, people need to united instead of everyone goes on different path. The proof are the drop of big fansites and the rising of wikia models in internet. I thinks that in future the wikia model will be more incorporated in more different things like games. United we stand, divided we fall!
Making a private engine is too stupid, less that 1% of people can complete they games, they eventually gives up and, generally, throw all made at the point away. If they made a private engine, not only the game, but the engine are lost.
On other hand, an important point is the RPG Maker XP limitations, like the ones that DarkDoom3000 neatly pointed.