If the Lumia is not announced tomorrow I will be concerned about its viability. If it does not come out first week of May it will be eclipsed by the Galaxy S4 launch. And if they wait until June it may look dated both due to the Catwalk, the fact it is based on a then 7month old design, and new designs will be out in Sep. Either way is a lose, right now is the time it needs to launch. All of the leaks, NDAs, etc are confusing as well if there is no planned imminent launch.
They could open the S4 up for preorders silently tomorrow (i.e. only if you search for the phone) and make the 928 a big frontpage launch. While risky, that is the only way to play this right IMO. Unless they have no intention of expanding the WP8 base beyond what it is already...