May of course not...since its too close to the WWDC...so its going to be an March event or WWDC
Apple doesn't have a deep need to launch iMacs during WWDC. At this point Apple has
four operating systems to cover at WWDC ( macOS , iOS , tvOS , watchOS ). If there is absolutely nothing substantive to say about four operating system then there is something colossaly wrong with their implementation strategies. When there was only one or two OS then sure fill something of the rest of the keynote with some hadware if had to flush out the time. That isn't a problem at this point. If anything the large dog pony show they do is actually too long.
In past, there has been some new hardware component drops to the market not because of WWDC but far more due to CompuTex ( which is a big major general PC hardware focused convention. ). In years past Intel (with little competition) would queue up their desktop / laptop releases for late May/ early June so that there was fresh, 'bleeding edge' stuff to show at Computex. They could afford to sit and squat to relatively arbitrary (to the hardware development process ) deadline of a annual conference so to make a bigge marketing splash. WWDC typically follows a week or so after Computex (it is more so a secondary indicator if coupled to hardware introductions. )
At this point there is more competition and their fab timelines aren't as regular. Intel has a logjam now on their 14nm process that should start to clear in March-April timeframe (adding new capacity and should be online by then). There is little upside to Intel waiting if fab is ready to go. Neither for AMD ( waiting around for Intel fab act together is kind of looney. The lead they have for 2019 product is going to close over time. )
Furthermore, June-Sept is a highly dubious time for Apple to release new hardware ( which typically needs new OS additions to be complete). From June-Aug Apple should be far more focused on getting the bugs identified in their beta release of the yearly OS for late Sept-Early October. Not chasing down new hardware quirks but far more focused on the hardware they got for the new OS they are getting ready to release ( and wrapping up any 'loose ends' on the OS they are about to push into the "no new substantive features" status. ). New hardware and new software means have two moving targets to track. That is generally
not going to lead to better stability for either subsystem. ( The increasing flakey releases by Apple over the last couple of years isn't particularly surprising. )
If the hardware just happens to finish at the same time (e.g., the major component suppliers are pushing them into that corner) then fine. they should try take measures to step out of that. But for Apple to "seek out" to deliberately push hardware into the next macOS beta window is at the very least dubious and probably a bad practice. November-April would be a better place to put more Mac product releases (and to do more of them. Not hit the snooze button for 3-6 years at a time. )
Picking WWDC as a release point is like a "broken analog clock". It is 'correct' about twice a day. On these forums from January to May it is increasingly throw out as something to attach just about anything non iPhone to as a 'safe bet' . Product xyz is important to Apple will attach it to WWDC because that is where important stuff goes... ... all the while completely ignoring that WWDC is a developers convention and the yearly OS updates are previewed there. (and now that there are many more of them. )
Apple built a multimillion dollar theater. They can do a dog and pony product intro with a major Internet broadcast any month they want to with a simple short stroll from their executive offices.