It's definitely possible to create a plugin with older technologies but that would mean big investments upfront and a maintenance burden in the long term (they need to be developed for Mac and Windows separately and use arcane programming languages from the past like Visual Basic).
So our decision to wait for the availability of this new add-in system seemed like the obvious thing to do last year. Now as it is still not available and even on Windows severly limited we regret the decision because it delayed this important feature.
I'm sorry for that. All I can say is that Word support is one of the highest priorities together with mobile Apps for us going forward.