So I sat down to play with some experimentation regarding the specifics of Shadow Form while at work today. I've come to the conclusion that although maintaining Shadow Form requires the use of a Superior Rune and a dedicated set of armor, it could well be worthwhile.
Rather than explore the use of an Elementalist as most tend to, I focused on the possibility of using the Mesmer Skill Arcane Echo (I briefly considered Arcane Mimicry for a pair of two assassins using the same build and copying gone another's Elite, but the recharge rate on that spell is too great to allow it to work), to create two copies of Shadow Form on the Assassin's Skill Bar.
First, proof of concept. At Shadow Arts 15, Shadow Form lasts for 21 seconds, or 25.2 with an Enchanting +20% weapon. This is JUST enough to work, but at Shadow Arts 16 it's more smooth, having a duration of 22 (26.4 +20%)
Arcane Echo becomes the next spell you use in the next 20 seconds, and after it becomes that spell, it remains so for 20 seconds before Arcane Echo's 20 Second Cooldown kicks in.
Shadow Form costs 10 Energy, lasts 26.4 Seconds, and recharges in 45 Seconds Cast Time: 1 Second
Arcane Echo costs 15 Energy, lasts 20 Seconds, the duplicate lasts for 20 Seconds, and recharges in 20 Seconds. Cast Time: 2 Seconds
The general strategy is to open with Arcane Echo(2 Sec, -15 Energy, +2.33 E Regen, Net Energy Change is -12.34)
Then immediately cast Shadow Form(1 Sec -10 Energy, +1.33 E Regen, Net Energy Change is -8.67)
You then have 19 seconds of time in which to take actions, attack (at -33% damage), and what have you. Over the 19 seconds, you will regenerate a TOTAL of 25.27 Energy, which is enough, not counting other activated skills, to bring your energy to a net result of +4.26
On the 19th second, you MUST cast the Arcane Echo Shadow Form, because on the following second, it expires. You should take along an escape skill or a defense such as Shroud of Distress to mitigate the destruction should you FAIL to escape (it can also help if you get Disenchanted)
(1 Sec -10 Energy, +1.33 E Regen, Net Energy Change is -8.67)
This time, you'll permit the entire 26.4 second duration of Shadow Form to run. Over the next 23 Seconds, you regain 30.59 Energy. Seconds 23 and 24 of the duration are devoted to recasting the newly recharged Arcane Echo(2 Sec, -15 Energy, +2.33 E Regen, Net Energy Change is -12.34), followed by the last second (with 1 second of overlapping leeway afterward), for Shadow Form's original skill(1 Sec -10 Energy, +1.33 E Regen, Net Energy Change is -8.67)
This build doesn't address other skills in use, but such things that might be easily combined with this setup could be Critical Eyes for adding Critical Hit chance and improving energy regain from critical hits, and attack skills that regain energy (There is a lead in and a dual attack that cost 5 energy each, and return more than they use, Also, the dual attack is automatically a Critical Hit in addition)
With Radiant Insignia's and all runes except a Superior Shadow Arts rune, Assassins have 25+16 Energy, or 31 total energy, thus this ability set is within their capabilities to use.
--- Opinions at present, anyone?
And yes, I did all this at work, because I was bored, using just the wiki.
Now I kinda wish my Assassin was named Ame