They've already stated that you can not transfer games from Origin to Steam. (other forum posts have replies from EA reps)
A number of the Steam releases still require Origin anyway. (SWBF2 for example). Steam will show in the description of the item if the 3rd party DRM and Origin Client is needed.
Many games require the Origin client regardless of where you purchase, steam, origin, etc.
Hopefully they will fix this and allow license transfers or remove the Origin-only DRM.
I'm still angry over being a pre-order collector's edition SWBF2 back at launch to watch them give everything for free, and now they want me to pay for it all over again, even on Origin "Anniversary Upgrade" etc...
Thanks for those exclusives back in the day, and thanks for continuing to make me not play it on purpose
(link to another forum thread I read before this one, https://answers.ea.com/t5/Origin-Client-Web-Technical/transfer-origin-games-to-steam/td-p/9206352 )