The harddisks inside can't saturate USB 3.1 Gen 1 at 5Gbps, so there would be only limited benefit at best to USB 3.1 Gen 2 at 10Gbps. SR's (limited) benchmarks show only ~364MB/sec in RAID0, which is within USB 3.1 Gen 1's transfer speeds-- or are you seeing more limitations than that in your own use? (if so, sources? I'd be curious, since I honestly haven't kept a very close eye on dual-drive external enclosures lately!)
I agree, you might see a limitation at peak speeds, but I wonder how much of that matters in typical customer use for these drives, given that sustained performance seems a more likely use case for a majority of the data transferred.