So it seems like the best answer is nerfing Lance and Cerberus, or altering in some way. I'd approve of this anyway, as they reside in the "S-Tier" of their respective categories, to the point of rendering other units pointless or unbuildable.
Of course, GoogleFrog has a very good point. A Lucifer buffed to the point of more general usability would have many of the same issues as Lance, or make it a static Lance to begin with. On the other hand, I could definitely see the sense in buffing Lucifer in non-offensive measures.
Speeding up seclusion into its armored form
It might be worth building if it cost 1600 or so.
Right now, Lucifer's uses are incredibly niche and often useless compared to Lance. I can recall one game I spectated months ago on Real Europe, where Galamesh had a Lucifer that was very good, but that was definitely not the norm.
I'd be a fan of a lucifer that went into its shell automatically, and was generally harder to kill.
For buffs on the offensive side, I think Lucifer would be best altered to have a much higher range(on par with Cerberus, higher or lower.) However, with the alteration of increasing reloadtime, possibly buffing damage slightly, but leaving it as is otherwise. I think this would mesh far better with it's armored form as is, giving it time to fire from a farther distance, making it harder to kill faster. This, I believe, would increase it's livability, and by extension ability for it to make cost. As well, this would serve to distance it from Lances, which would have even higher DPS over Lucifer, but lack range in comparison and be much more counterable, as Lucifer can be terra'd up as well. This would also contrast Lucifer more with DDM, though that isn't really needed. Lastly, it would make it more suitable in some situations over Cerberus, which would add a welcome third addition to the escalation that is essentially Lance/Silo/Cerberus.
However, I do believe nerfing and/or altering Lance and Cerberus would be a better option, and for Lance, needed in the first place.