Yep, no mention so it is an afterthought. While 2018/19 has been mentioned that could well be a start date. The bridge would have to have the height and span to allow anything that can get to the apron now to still get there including the new Dreamliners which spends time in TUI's hangar.
The question will be who and how will it be funded. The airport has done well over the years with government funded infrastructure projects but those funds can take years to materialise. I think the Airport Way upgrade was talked about for 10 years before the grants came though.
Worth Googling "Gatwick airport bridge images" as crossing taxiways has been done before.