yes, a pistol gripped M4 butt stock is not ideal for bayonet use. its something that was dealt with in SP school when we learned bayo use on the M16A2. so yes, i have been trained in bayonet use. however the butt stock is more ideal for CQC (i dont know anything more CQC than home defense) so that is a trade off that i am willing to take. the bayo will not the the primary use of the weapon, but is an option that i am willing to leave open for situations where a shot would not be ideal. i have seen some bayo mounts in use on various shotguns both mil and civ uses so i know they are out there, just havent found some to suite my needs yet. (i havent had a chance to check the links yet). oh, and good rifle fighting techniques can be used with a naked rifle, shotgun, or on a weapon with bayonet affixed.
Bayonet? Where a shot would not be ideal? If you're going to stab/jab/slice someone, you're committed to that level of lethal force, which is right up there with taking the shot. Deadly weapons are deadly weapons. There's also a lesser chance of actually neutralizing the threat, which is a kickass way to set yourself up for a lawsuit. That's also not to mention how ridiculously long it will make the stick. I'd REALLY reconsider that.
Find a place to take a basic shotgun course with the money you'd spend on the pistol grip M4 thingy-majig. You'll thank me for it.

As we say, "Learn to shoot the thing before spending another dime on it." There are safety courses everywhere that teach you the legal ramifications of the use of force, both criminal and civil. Figure that in most places, a jackass entering your home is committing a felony...which can also put you and the family in jeopardy. Your home is your castle, learn how to keep it safe.
the forend is the big thing that i am looking for.
IIRC I saw them at Brownells. If you're looking for a flashlight holder, there are others that attach right to tubes. For a mag extension, look no further than Wilson. Everything else attaches with a clamp to the barrel, which tends to put stress on everything. Not good.
The setup here is a factory 18" barrel with a front bead, Wilson 2-shot extension, Vang Comp Systems oversized safety button, and a stock I shortened about 2.25" for a shorter length of pull and better manipulation. After running through some courses with it I've seen other people remove frilly crap on the spot because it did NOT suit the mission, added weight, and was downright gimmicky. The simpler, the better. When I got rid of this one a couple months ago I was only planning on putting a clamp mount on the mag extension to hold a simple SureFire G2 light and a pressure switch attached to the forend. Silly lightweight, easy to move, nothing to hang up on, and with the standard stock it's much easier to manipulate the safety left and right handed. Pistol grips usually just get in the way on firearms they weren't designed around.