Nah, if this follows what Broadcom has done with their other XStream deployments, it's two AC2600 class radios on the 5GHz side, so no bonding... will be fine with GiGE, and no LAGG needed..
But the practical wifi rates. Thiggins say you can get 50% practically while i say 30%. but even 30% of that 5 or even 4Gb/s (talking about maximum achievable performance) will exceed 1Gb/s so having at least 2 ports teamed up would prevent ethernet from behind the bottleneck.
So the router will have a better working MU-MIMO and 2 5Ghz radios (8 streams). That means i could have 4 wifi clients each with dual channel MU-MIMO AC wifi downloading/uploading from a file server all at the same time and a single 1Gb/s ethernet port cannot keep up. Many embedded NAS now have multiple Gbe ports or even 10Gbe so LAGG would actually be very useful with at least 2 ports. Even so i still think that wired router + switch design is very poor because taking a typical wifi router:
[Wifi chip]------(bus/PCIe/similar)-----CPU-----1Gb/s-----[5 port switch with 4 ethernet ports and 1 port to the CPU]
Also connected to the CPU is a 1Gb/s WAN port.
On a hardware accelerated router
[Wifi chip]-----[Accelerator chip]---RGMII (1Gb/s)-------[5 port switch with 4 ethernet ports and 1 port to CPU with 3 RGMII interfaces]----1Gb/s----CPU
Also connected to the CPU is a WAN port or accelerator chip + WAN port. Wifi to wire traffic bottlenecked by the 1Gb/s RGMII interface which means that if i properly had 3 or 4 streams connected and they were all MU-MIMO including the wifi chip itself it will not go beyond 1Gb/s. You can test it yourself by bridging 2 AC87U together very closely, combining 2 ethernet ports at each end to a computer with 2 ethernet ports each and start stress testing to the point where the CPU is maxed out and the NICs are filled with packet queues trying to send and recieve at wirespeed. I recommend disabling windows network autotuning if you wish to test this.
This really limits throughput on WAN and in some cases also on LAN. If they keep to these traditional designs they are going to ruin the hardware performance potential since the bottleneck would be in the busses between the chips. Sure the accelerator chip on wifi with connection to the switch chip does reduce CPU load but than again only 1 Gb/s to the CPU? Even with wifi practical speeds being low but i managed to get 90% of the theoretical wifi bandwidth by stress testing in a nonsensical way to the point of dropped packets. If i see dropped packets and a low wifi utilisation that means that there is a bottleneck within the router which i think this AC5300 will have if you truely stress test it. I'd be happy to actually prove it if they release it with the traditional hardware design and lend me one using one of my nonsensical stress test by pairing up devices in such a way that the transfers will actually exceed the router's LAN capabilities.
My suggestion for the AC5300 would be if ASUS ever read this is
[Wifi Chips]-----[Accelerator with same arch as CPU such as with the AC3200]-----5x1Gb/s RGMII interfaces teamed up----managed switch chip with at least 8 RGMII and at least 8 ethernet ports----at least 2 RGMII to the CPU----- 2x WAN ports. This would be a significant upgrade obviously.
Another solution would be [wifi Chips]-----PCIe 2.0 at 2x at least------CPU----PCIe 2.0 at 4x at least or 8 RGMII interfaces-------managed switch chip with PCIe or 8 RGMII and 8 ethernet ports, 2 WAN ports connected to CPU as usual.
Perhaps some gadgetry like esata and a much faster CPU, perhaps a SoDIMM RAM slot so you can use laptop RAM with it and get as much memory as you want/need. Maybe the CPU could be swappable so it can be upgraded to a faster CPU if there isnt one that properly supports this. From a consumer point of view for that much wifi bandwidth there will be LAN media transfers, file transfers, gaming and ofcourse lots of internet stuff for the same reasons which means having 2 dedicated WAN ports would fare a lot better in throughput with a much faster CPU and a better internal design. It means being able to have 2 gigabit ISPs at the same time properly on a consumer router with enough LAN ports and users to actually utilise it.