It's a really excellent question - I'd heard originally - I believe it was from others who'd spoken with Lotus USA but could not swear to it - that the engine choice for the US version Elise would be announced in or around July, and the rest of the specifications would be released subsequently, and pretty much all would be known by October/November time frame.
We're all eagerly awaiting official word from Lotus on these details, but so far it's pretty much rumours. We all just need to try to be patient, and it's not easy !
A few months back word from Arnie (Louts CEO) by way of the local GM was July for the motor and Nov for "full" details. Lately I've been hearing mid-Aug for the motor at a Lotus owners meeting. If everything stays on track, first orders will go in Jan. so it would make sense for Nov/Dec to have full details maybe even sneak peak write ups by the mags.