I think GSX will make it necessary for AES to be updated graphically to be able to compete.
AES is way behind on visual appeal.
Oliver has been working on AES NG for a while.
I was thinking about this a little more the other day. With AES, Oliver customizes every airport and my understanding is that the jetways are a large portion of the workload. That's what you are paying for with AES - jetway animation and customized pushback (AES has different pushback paths for most gates). Since GSX's pricing structure is different (one time fee I'm assuming), there is no way they could provide AES type jetway animation on a global scale. FSDT would have to customize every single airport which of couse, isn't possible. I do, however, think a rewrite of the FSX jetway animation would be awesome and doable. It would be a big selling feature for me and I think it presents the best opportunity for GSX to dig in to AES market share.
So in the end, it sounds like GSX will be global solution and AES will continue to be a local, more customized solution for specific airports.