I'm guessing that's why they're printing new cards. Otherwise, it seems rather pointless, but perhaps it can be financially justified as part of a "look, we're now in the Star Alliance" campaign.

FWIW, I have occasionally been required to show my "Skyteam Elite Plus" card for lounge admission overseas.

BTW, my impression is that the overseas Star Alliance lounges will be a bit better than the SkyTeam lounges. Like Lufthansa always seems to put out a better spread in their lounge than does Air France.