: One of the things that bug me about Reach is that it 'modernized' the
: weapons, and took them a step backward. With the MA5 series, I can imagine
: that there's some sort of futuristic attachment system that beats the
: socks off of Picatinny rails and stays hidden.

Wouldn't you want it to be simple though? The first video above makes a point of saying you can assemble and disassemble the gun without tools, and if you feel you need one you can just use one of the rounds it fires, and I've heard that said about other guns before. Mechanical attachment is robust too, it's relatively easy to make it strong and durable. They could have some futuristic thing that works as well or even somewhat better and is just as easy to use but there might be an issue of cost.
Did you have something in mind? I don't know what they could use besides some kind of rail attachment, latches, hooks, screws, or magnets.