(03 Jun 2020, 9:47 pm)streetdeckfan wrote They're in the same boat though , same with the 63 plates, they're essentially the same albeit a few years younger. Still can't upgrade them to Euro 6 and they're still expensive to run and maintain.

I personally doubt the 63 plates will see a mid-life refurb either, more likely that they'll get sold off and replaced.

How can a vehicle which is 4 years younger than an acquired vehicle, is of a higher spec internally and also more than likely have a higher book value - be 'in the same boat'?
The Yxxx ERG Solars went before the NK54 xxx Solars for a reason and it wasn't just because of the Eminox upgrades.
Ditto the Vxxx ERG MPD's and the NK53 xxx MPD's.

If the Citaros start to go as you say, it will be the older ones and it will be done over a period of time. By the time they get to the 10 plate Mercs, they're going to be hitting the 14/15 year old mark - which means that they're just 2/3 of the way through their working life as it stands. 
The 06/07 ones are more or less at that full-life stage already. 
As for the 63 plate batch, I'd expect them to be coming towards a mid-life refurb and paint-job.