Also remember that should that happen you most likely are going to see the same thing happen to MSTS II that has happened to Trainz.
Obviously the Trainz graphics engine has it's issues, but one of the biggest reason for poor performance (except on the latest computers) is the extreme poly count of 3rd party assets.
Yes the default Auran content is at best basic, however the poly count is about as low as one can get it. The more polys a computer has to display the harder it has to work. At some point it's too much, the computer just can't keep up.
If Microsoft and Auran both locked down their games (allowing no custom content) and did everything themselves you'd probably see a huge increase in performance. However, these types of "games" just wouldn't work without the community. But, at the same time it's also the cause for the problem. Though from what I'm told, I'm not so sure game companies take care of their own stuff now.....
What's going to be the biggest turn-off for MSTS is most likely going to be the fact it will be Vista only. Yes, yes we all know that 99% of computers come pre-loaded with it. BUT, this doesn't mean they stay that way. Most Vista pre-loads I see come to me to be wiped and loaded with XP xxx. Those that know about computer tech haven't even loaded Vista for obvious reasons. Yes it is the next step, but until MS can get it together there is zero reason for those with XP to upgrade. The Vista only will probably play a huge roll in MSTS II's popularity to the mass public.
P.S. Even if MSTS II is superior in every way to Trainz, you're also going to need some major cash for a new computer that can handle both Vista and MSTS II
Vista can take anywhere from 650MB to 850MB of system RAM on idle, as well as up to 35% of the CPU. A superior game will need a superior computer. For those that are truely interested in MSTS II, downloading the Flight Sim X demo (or buying the full game) will give you a pre-view of what you can expect as far as performance and visuals.