A customizable visor HUD actually sounds really cool. It adds another layer of identity for someone's MP Spartan, and maybe you could change around UI elements to suit your own personal preferences. You could maybe change the color and have a small selection of varied visor "styles" you could pick from.
Just don't count on it. A customizable visor, as cool as it sounds, also sounds like a reaaalllly small niche that 343 probably doesn't have in mind. Different visors were introduced in 5's Campaign alone because of the nature of that Campaign, and given the general contention with that title, I don't think its really an idea 343 looked at and decided to go with. If anything, I feel like customizable visors would be on the backburner of customization options they'd be providing to players.
Sooo...yeah, just don't have an expectation for customizable visors. But hey if I get to have a rainbow HUD while I make a zombie a new hole sure, I'll happily be wrong