I'm going to wait and see. Considering this is Lionel, after they're released, after all the complaining about this is wrong and that is wrong, and after everything settles down, then I'll think about picking up a set.
Unsolicited sharing of Just a few thoughts....
1. Lionel seems to be putting a lot of investment into their 21" cars. This means that for better or worse, I think they will be making them for a while. Scarcity in the near term should not be an issue.
2. If they're wrong, incorrect, or whatever then there will be a lot of them available at much better prices than the advance build to order hoo-ha. Similar to the eBay glut of renumbered FEF's that were rejected due to incorrectly advertised feedwater heater systems. I suspect inaccurate details aside they would still be a nice set to pick up at that point, but at a much better price. Remember all the hubub about the 18" aluminum cars? and now it seems nobody wants them.
3. I'm optimistic that Lionel will get it right and hits it out of the park with this set then (see #1) I'd wager that they will be available in the next few catalogs anyway (i.e ESE) and I will feel better about putting up bigger money after seeing the actual production models.
The rest, as I've mentioned, is wait and see. Besides I have two sets of Harriman cars on order I have to pay for first.