still somewhat of a newbie to airsoft generally, so I obviously won't say anything internal related, just pitching in a few aesthetically related features. With bullpups, I've always thought the weight balance and center of gravity resulting from the arrangement would help a lot with reloading efficiency. the only thing that annoys me about most bullpups is the fact that the mag release is always sitting next to the magazine, sort of kills the convenience. i mean, think about it, you think it would be more efficient to have to reach back and grab the magwell to pull out a mag, or just push a button and give the rifle a shake like a M4? (Conventional rifles, I wouldn't nag about this since your hand is already near the magwell anyways. Bullpups have more of a stretch though.) going with that, what do you think about fabricating a custom, long mag release that extends forward to the grip area, as opposed to putting a release button around the magwell? IMO, that'd be more efficient when reloading.
(before you say anything, yes, I can immediately tell that shaking a mag off a M4 is stupid in airsoft, you want the mag going in a dump pouch of course. In the instance of a bullpup rifle, however, it really seems practical to me since the mag is in the back of the rifle. Keep the dump pouch on the same side that the rifle is shouldered, and drop off the mag by just unshouldering the rifle, jutting it back a bit, and pressing a mag catch.)