It's one of those Multi-purpose builds where you can be either a really good anti-aggro controller, a really good "Buffer/Healer" or a hybrid. Good hybrid builds are possible but require more skill to play, as well as being much more expensive.
No, you won't be soloing AVs, but depending on your build you might be able to tank them with PA and Phantasm's Decoy. You should be able to contribute decent damage to taking one down, depending on build + slotting.
I've an Illusion/Empath which has Perma-Adrenalin Boost and is a few seconds short of Perma-Phantom Army. It was rather expensive, but makes a very good all-round support toon hybrid.
Blind and Deceive are the control powers you'll be spamming. The Purple Confuse Proc in Deceive will turn it into an AoE control. Spec Terror and PA are your main AoE controls, Flash has a fairly slow activation time for what it does but it might be useful depending on your playstyle (it doesn't suit mine). Empathy Powers are the usual slotting. The two Auras, Fortitude, Clear Mind, Adrenalin Boost and Heal Other being the main contenders, with at least one Endmod in AB to let Blasters recover End through a Nuke. Healing Aura makes a nice self-heal and Absorb Pain is for when your tanker is about to get two-shot.
One of the reasons for still going for an Empath Controller over an Empath Defender is the Controller Epic Pool version of Power Boost - it's up twice as often, which means twice as many power boosted Heals or Forts. It still helps to take Invis these days, but with the +Stealth Procs there are other ways to get there that don't cost as much endurance as Superior Invisibility.
I've not bothered with Empath PvP in ages since Diminishing returns came in. In days of old Ill/Empath was a good PvP support toon because of Superior Invisibility masking it from most Villains in Sirens Call. I suppose it's be just as good as any other Empath these days. Illusion has a fairly wide range of controls to fall back on too.
What is an Ilu/Empath in groups nowadays? A little bit control, a little bit heal?
Also, we can't really solo AVs like Ill/Rad, right?
And is Illusion/Empathy any good at PVP?