Part of the Furniture
I wish they were promising at least security updates... Fw upgrades was what made me abandon my old AC56U that was suddenly out of support, while other sibling models had really longer life....
Maybe an S version would have shorter upgrades... Though they are currently the same FW as the U model.
I like to think that the economical trick, if there is any, is to go with the 'mainstream' model that will serve well over time, sell many, and enjoy the longest firmware support (security updates). The AX86U may be that and the AX86S using the same firmware package may go along for the ride. And you pay a bit more for that than you would for the lesser models (or maybe you don't if it allows you to plan your purchasing to suit the/your evolution of technology and not have to rush out and buy sideways to get your network back up).
The N66U, AC68U, AC86U, and now AX86U have hit this mark for me... except the AC86U has disappointed by burning out prematurely... it happens.