Yes, L113s may appear. That is what happened to service 963 a
while ago. Sighted a few Scania L113's on the streets near Upper
Bukit Timah Road.
If you really wish to know whether Service 966 would use bendys,
those staying in Yishun may get to the Yishun Interchange early,
about 8am, on the Sunday, on the date Service 966 would be
launched.
Look at the bendy's bus park(where Service 851 and 854 bendys
always park), if you're lucky, and I mean real lucky, you may get
to see some unknown(not from Yishun) bendy's displaying the 966
electronic rego. Saw the same thing when Service 963 was
introduced. These buses would later depart for WRI, I believe. The
bendy (TIB 1222 C) I took later on Service 963 was one of the 2 I
saw parked at Yishun.