Why not make longcat/tacgnol GRAY with the cat in black/white? Make them proper profile for ENTER and PLUS, and wacko keyboard people can deal with one being a bit off profile?
Well the problem is that it really depends what people are trying to do with them. Since I'm buying both, I wouldn't mind them both being grey background but most people either have white or black keyboards/keycap sets and would probably rather have the one that matches, or will only buy longcat because they don't really care about tacgnol, which is a meme inside a meme. If they are just getting one of the two, then it makes more sense for them to both be enter, since only having a + would be odd probably.
The wacko keyboard Kinesis people like myself is the reason that I had first suggested the tacgnol, because I have two numpad enters that are facing each other, which is what the famous longcat/tacgnol meme picture is about. If you've got a normal numpad, buying both to stack them on top of each other kind of defeats the purpose of the meme, and it's better that you just get the one that suits your color scheme best, or get them for two separate keyboards, since most of us have a bunch anyways.
Also, for the wacko keyboards, the numpad enters are space and backspace, which are two really common keys, so there is no way in hell I'd be able to deal with them being off profile whereas for people using it on a numpad, having numpad + a little off is much less of a problem.