I don't consider WiFi to be a necessity on buses these days, except for on Megabus, National Express or any other long distance coach operators. Most people have unlimited 4G in their mobile phone contract plan.
USB charging points I think are a necessity mind, because I for one am regularly on my phone, whether it be work, social, or whatever (and for bus spotting/checking timetables!), and yes, whilst I have a portable charger, if buses are equipped with them it saves my portable charger for a time where I am least likely to have access to a charging point.
I find it ridiculous that in London only the 507, 521 and X26 have USB ports, the latter of which is only because it's a long route and I don't think Croydon's WVL's were equipped with them from new. About time the X26 had an upgrade actually on the vehicles in general, but obviously that's not for this thread.