I am glad to hear that the ICYBento MB559U3S-1SB has not been discontinued. I am an IT consultant and use the ICYBento series exclusively for external server backups that are rotated offsite.
Regarding USB 3.1 gen 2 and USB-C, the advantage of USB 3.1 gen 2 is the speed of transfer. The ICYBento eSATA 2.0 port only supports 3 Gbps with 8b/10b encoding, which consumes 20%, leaving a maximum of 2.4 Gbps (it should be trivial to upgrade a future hardware revision to eSATA 3.0 running at 6 Gbps). USB 3.0 (now renamed USB 3.1 gen 1 in what has to be the least intelligent marketing move of the past 7 years) supports 5 Gbps and also runs 8b/10b encoding, which makes for a maximum transfer speed of 4 Gbps. USB 3.1 gen 2 runs at 10 Gbps with 128b/132b encoding, which only consumes 3%, leaving a maximum transfer speed of 9.7 Gbps. In all cases, the real world transfer speed will be something less than the maximum. It should be noted that none of the existing connectivity options on the ICYBento are as fast as the internal SATA 3.0 6 Gbps hard drive connection. eSATA 3.0 6 Gbps would solve this problem, as well as USB 3.1 gen 2, at least until we switch over to SATA 3.2 (also known as "SATA Express") running at 16 Gbps.
USB 3.1 gen 2 can be implemented over USB-A/USB-B ports, or over USB-C. The advantage to USB-C is that more power can be transferred over the cable. All USB 3.x powered ports are required to support a minimum of 900mA at 5V making a total of 4.5W. However, USB-C also supports 1.5A at 5V and 3A at 5V. This is distinct from the USB Power Delivery 2.0 spec, which can push things up to 5A at 20V. Because most USB-C devices will likely support quick charging via 3A at 5V, I am assuming that as USB-C ports become common on motherboards, the manufacturers will power them at up to 3A as a standard configuration (I know, it is always dangerous to assume things). That provides a total of 15W. The current ICYBento power supply provides 2A at 12V for 24W, but I would imagine that in most cases 15W would be sufficient to power whatever is inside the enclosure. Therefore, having a USB-C option on a future hardware revision would allow for powering the enclosure VIA the USB cable making the power supply optional.
As long as we are on the topic of cool things that I would like to see Icy Dock manufacture in the future, I have two further recommendations.
Build a variant of the ICYBento in the 2.5 inch form factor. Something along the lines of of this Anker model.
Update the DataCage Classic MB454SPF-B to have a SFF-8087 or SFF-8643 connector. The current connector for hard drive failure light information is not compatible with any RAID card worth having. Switching to one of the more modern connectors would be a common sense hardware revision to keep up with the times. (I would recommend this change for all of your hard drive cages. In fact, if you only have time to implement one of the changes mentioned in this post, this would be the one I would prefer.)