If that's the case SBST should have directly replaced all the JB
MK3s with K230UBs back in Aug 2011. It seems that the efforts of
registering the DM3500s with JB and making rectangular side destos
for 160/170 had gone down the drain if 160/170 is to get full fleet
K230UBs soon.
I think you missed out the point you raised in your post. Think
about it, they could have used the Mk4 DMs & Striders to
replace the outgoing JB Mk3s back then, but yet they picked from
the later-registered DM3500 batch instead. And for the handful of
Striders that were touched for JB, they are the last few of the
Striders.
It's quite an obvious reason why
they picked the last few Striders reg-ed and not those Mk4 DMs or
19xx-series Striders - the lifespan expiry dates.
And then if you take a step back, back then when they decided to
use DM3500s to replace the JB Mk3s, there was only a limited number
of Citaros. The KUBs formed the bulk of their SD WAB fleet. The
thought process for the JB fleet renewal is definitely not a
one-month exercise, they probably planned for ages and didn't
foresee that 160 & 170 would go WAB anytime soon.
So what to do then if that's the case? Pluck the newest non-WAB
SDs then, which is the DM3500s & the last few Striders.
Then now with the first few DM3500s due to be gone soon within
the next 2-3 years even with max extension, they can only pluck
from the next set of newest buses, which is the KUBs. And it
becomes inevitable that 160 & 170 will go WAB-status soon.
