If the X7 ever was to receive an upgrade, if the engineering was up to standard at Deptford (home depot) and Peterlee, then Streetlite Micro Hybrids could be an option. I know that the lightweight chassis isn't as comfortable as a full on heavyweight chassis but, in terms of reliability, it would depend on how GNE looked after them and if they did, then there'd be none or very few issues.
Mind you though, I'd still say heavyweight deckers (Scania) when it comes to replacing 6043 - 6048 in a few years time due to the sheer amount of passengers being carried and the tougher operating and driving conditions that are encountered.
RE: Go North East: 2015/16 Financial Year Order Predictions