You should definitely THINK about your (paying) customers if they REALLY have production systems on MacOSX, which REQUIRE a business process engine.
Where there is no need for a business process engine, why should there be a need for a business process modeler ( which is just a free gift ) ?
So do you really see your customers want to use the commercial BPengine on MacOSX, with what applications & use cases ?
Especially if your software base can´t be transfered easily to Linux, why should you have a try with MacOSX which is a BSD Unix ?
So if there was no Linux solution, why should you NOW try to create a MacOSX solution, just because iPhone ( not Desktop Mac! ) is so popular ?!
Please CONCENTRATE on your main topics & main unique selling propositions ( USPs )!
So if you are stuck on Windows, please accept this.
With new rendering & GUI framework technologies, you might have a try to make a product which runs everywhere ( WIndows, Linux, MacOSX, Android which differs much from a just-LInux, Win8Phone-Metro / iPhone/iPad which require different GUI than the corresponding desktop PC platforms ) don´t know much products or frameworks which allow this,
and especially if this technology is not the base for your application,
such a move would cause a total recoding... without any benefit for the WIndows users.
But be warned that there are already competitors which enable the customers to do all BPMN / EPK modeling in an Internet browser, with a SAAS - Cloud server-based application ( Some or even all of all of these competitor - at least in your product-cost class - just have no business process engine.. though a server-based process engine - on the customer's server of course, mostly not on a SAAS - Cloud Internet server - is the real bargain if you take the burden to do business process modeling)
If you don´t wanna go this way to move to a Total-Browser-Solution ( would be intersting of course, though ) - then please stay on Windows, or you are LOST due to much work without benefit for anybody.
Btw, if you could integrate your products - both modeler and engine - on a platform like SalesForce as paid Third-Party Services hosted by Salesforce ( and I mean SalesForce as #1 SAAS-Cloud business application platform ), this might be a real breakthrough - as then the SAAS-Cloud based engine would call other SAAS-Cloud services but which are not on another remote slow internet server, but on the SAME cloud farm, so accessable as fast on a local company datacenter.