I was quite surprised to see this one retire so early (being one of the not to be converted units) but that will explain it. Potential for a quick C4 to prolong its life or shortly to find its way to Long Marston?
To get all the material together for a C4 now would be very hard, the contract for the last round of C4s having been completed, a new contract would need to be tendered and awarded and the material overhauled, some parts having a lead time of months for the quantity needed, so I doubt quick will be a word used.
The work now will be starting to get motor wheelsets removed from the last C4 unit 8501 reconfigured with 100mph gearing I would think. 8534 had its C4 with 5 car conversion, 460004 (which 1/2 became 4/5 of 8534) was the only ex-460 to need one. 8006/8012/8013/8014/8015/8017/8021/8022/8023 also had a C4 as well as conversion but have more miles left in them than 8534, 8534 being unit 1 and the others being in the group units 25-36.