Attract Mode 2.5.0 does work for Retropie with Raspberry Pi3B. (Note: I'm not using the Pi3B+, so can't comment on that).
Make a backup of your image first.
I originally started with Floob's implementation/image of Attract Mode, not the experimental version installed via Retropie Setup, so I don't know whether the method I set out below will work for the latter implementation.
Enter the following commands in order in the terminal (ie exit out of Attract Mode to the command line):
(i) attract -v
(ii) killall -9 attract
(iii) cd ~
(iv) rm -rf develop
(v) mkdir develop
(vi) cd develop/
(vii) git clone --depth 1
https://github.com/mickelson/attract attract
(viii) cd attract/
(ix) make USE_GLES=1
(x) sudo make install USE_GLES=1
(xi) attract -v
(xii) sudo reboot
These commands successfully updated Attract Mode to version 2.5.0. Note that none of the personalisation was touched by the update. The "autostart.sh" for Retropie wasn't touched at all, nor was the attract.cfg file. Everything therefore worked perfectly for me.
