I've pre-ordered trains since - oh - 1974??? I ordered the Lionel Spirit of '76 set from Alison Cox of Seattle fame nearly a year in advance as the first Spirit trains were released in late '74/'75.
Problems pre-ordering over the years? No, not really. Regrets, ever? Nope, not really.
If I want it and can afford it, I order it.
I've pre-ordered quite a bit of SP stuff from Lionel over the past year or so. The trains are arriving. Problems? Nope. At least not yet.
If I were to think of not pre-ordering, thoughts would go to Lionel's SP Lark loc (now in my possession) and how very quickly it will be UNavailable.