It was me that wrote the business case for Skylink Express so I feel a great affinity with it and may be able to assist people's understanding.
The availability of the coaches was certainly convenient and shortened the lead time for introduction, but it wasn't the deciding factor - far from it. The project appraisal process in Wellglade is very rigorous indeed and any potential project has to make a compelling business case - the idea of using assets just because they happen to be available would be complete anathema. In this case, the possible use of the coaches on Skylink Express had to be tested against all other possible scenarios, including simply selling them off as well as other possible route innovations. The plan also had to take account of the likely abstraction of revenue from Skylink Nottingham.
Of course I'm not there any more so I have no idea how it is currently performing and I certainly wouldn't breach any commercial confidences. But I can say that the business case recognised that it would take a long time to grow, and this coupled with the strong relationship between trentbarton and EMA meant that any review of performance will take into account performance over a much longer period than might be the case with abnormal commercial bus service. Importantly, the combination of fares and journey time means that the break even load is a lot lower than you might imagine.
Apologies if you've already read it, but there's a lot more on the subject here if it's of any interest:
http://philstockley.blogspot.co.uk/2016/01/skylink-flying-high.html?m=1