I would prefer it if the loop around the Interchange
is converted into a feeder service. Something like this:
Service 859 (the service number may have to be changed)
Service 880: Loop service serving both directions
This amendment might be actually feasible; rather than try to
make route 859 a Sembawang feeder and Sembawang-Yishun inter-town
route, it could make sense to split them into two routes and extend
the shell of the former route 859 (now relieved of it's burden as a
inter-town/feeder route) to somewhere else - Changi Village (as
suggested), Changi Airport, or Tampines. Might also help allievate
some of route 969's load if extended to Tampines.
Coupled with my enhanced route 856 (which will turn it into a
true part-time inter-town route between Sembawang and Yishun), and
the through-fare system, your route 859/880 suggestion might work,
though some residents might complain of loss of direct links
between Sembawang and Yishun (those in Sembawang Crescent and
Admiralty Drive neighbourhoods, especially). And yes, route 859
might need a new number. Route 989?! (Random suggestion, lol)