Something that annoys me is how people seem obsessed with looking "authentic" and how they think you absolutely need to provide unique box designs for every region (and of course both "old" and "new" designs for each, since the designs changed halfway through the console's lifetime). Does anybody realize how much of an inventory hell is this?
Worse yet, there's the trademark infringement issue — they just look too close to the official Sega designs, and Sega definitely has trademark on those again nowadays (both because of Sonic Mania and because of the Minis, not to mention all the Mega Drive merchandise). No, using "16 BIT CARTRIDGE" doesn't change the fact the design is still too close, if anything it only makes it look like a cheap bootleg.
Also, it's not like we're selling these games at local stores that you walked in and looked at the shelf for a game to rent or buy, but rather at on-line stores that sell globally, if not outright a Kickstarter campaign. That also kills the "authenticity" aspect really hard. On top of that, our new games look nothing like the ones from back in the day, as our culture has changed a lot since then.
Can we just admit that this isn't the '90s and acknowledge we're doing a whole new thing?
So what then?
I'd honestly prefer if we just dropped the Sega-like designs and let the game artwork fill the whole box. When we aren't pretending to be a Sega knock-off the boxes will look a lot better and feel less "bootleg", and you avoid risking the anger of a lawyer who may be in bad mood that day. Also, it means you just need a single box design and won't need to worry if you sell too much or too little of a given edition.
Acknowledging that we're a global market (if niche) also means no region lockout. Thankfully I haven't really seen trouble over this yet, but it means you should always consider "universal" shells when possible (those that fit in both Western and Japanese consoles). This way nobody has to worry about whether a game will work in their console or not, and again the inventory benefit of not having to worry about multiple editions.
Also don't forget to check out commercial homebrew guidelines in this site! There's some useful advice there, coming mostly from previous experiences. Learn from our past mistakes and you'll make everybody's lives easier.