The idea of an external optical drive is not new by any means, but they can be useful. This is especially true if you have multiple computers. I would argue that average users should still have a CD, DVD, and potentially Blu-ray drive, maybe even one with writing capabilities, but I think we're long past the point of needing a dedicated one for each PC.
OWC has just announced two new models, one with a 24x DVD burner, and another with a 16x Blu-ray burner (I think this is the right link???). Interestingly, the press release states that they are compatible with USB 3.1 although a 16x Blu-ray transfers at 72 MB/s, which isn't even close to USB 3.0, let alone 3.1. I should note that the product pages seem to state USB 3.0, though. It seems a little silly to go for the higher-end link, but maybe it didn't cost them anything, so why not? They also supports the M-DISC format, which uses a high-durability medium (instead of the typical metal foil) that is supposed to not degrade for hundreds (maybe thousands) of years.
OWC also sells a 3-pack of 25GB M-DISC discs for about $15, which works out to about 20c/GB. This isn't too bad but, with cloud storage being in the ~3c/GB range and external harddrives in the ~4c/GB range, it might be of limited use since you could just make like 5-6 copies per M-DISC copy. You will also need to consider whether you will have the ability to read these discs in the future, although similar considerations must be made for all storage archival solutions (will AWS be around in 50 years, etc.). It might make sense for some, especially enterprises, though.
These drives are available now.