DLC purchased on Steam not usable on Mac + conflicting EA support guidance

luckyyghoul​  I guess that depends on whether EA is ever motivated to renegotiate the license with Steam.  It's never happened for Sims 3, so maybe not, but anything is possible.

As for whether this is intentional, I would categorize it more as a known side effect.  I very much doubt that EA decided to block the content outright.  Rather, this is a forseeable outcome of a decision about a different matter and is apparently not important enough to try to find a solution.