When I was there in October, the majority of the rides we went up to the CM at the FP+ entrance, showed the baby and received a Rider Switch card (like old FP cards). It was good for a week or something.
For Splash & BTMRR (in particular, maybe other ones too) we got a lanyard, and were not presented with a Rider Switch card until we got to the FP+ merge point somewhere in the line. I would imagine this prevents people from exploiting Rider Switch (i.e, never waiting in the standby or FP+ line, just sending 3 people through once...not actually switching riders).
Overall it worked well, but we did spend a ton of time waiting for everbody to go twice, but out in the open not confined to the line.
Also, you can use Single Rider + Rider Switch if you want, thats what my friends did - as long as somebody goes through the Queue (standby, FP+, or Single Rider) once you can swap riders.