I suppose a DM could interpret that as only the power persists, not that anything else on sustain line happens (though maybe the caster could still choose to use the sustain action, in spite of the 'instead' phrasing). Lucubration doesn't actually say it makes sustain a free action or not an action, it just changes the power to 'last until ...' which is not how sustain is usually phrased. Given that interpretation (which seems a bit tenuous to me), the interaction would mean that you could use the Gaze on one turn, leave it for one or more rounds w/o repeating the attack (which would normally end it) meaning the target isn't dominated for that time, then come back to it and re-establish the dominate as long as you don't miss. Which'd be a little weird, since the overall gist of the power seems to be that you can establish domination (guaranteed - if you miss, initially, you can try again) and hold it for a time, then it's over for the day, so start-and-stop domination seems out of character for it.
The more obvious, but OP-seeming interpretation is that it makes sustain not an action, so the sustain line just happens on your turn, every turn, even if you're stunned or otherwise unable to initiate an attack. So the interaction would be that you repeat the attack on your turn, every turn, until you miss or go unconscious or the encounter ends - the target being out of range, out of pay, behind blocking terrain, or whatever, on your turn would prevent the attack, since it's still a ranged attack, even if there's no action, but since that's not a miss, the power wouldn't end, the target just wouldn't be dominated until the attack became possible again. Also a tad weird, for the same reasons.
Lucubration has always seemed a little nuts that way. What if you cast Lucubration on one round, and then Witchbolt all fight long? You could have bunches of the things buzzing away at every enemy that stayed anywhere near you. Or you could put up zones and play pinball. Or you could throw up some Sustain Standard effect that usually precludes attacking for that reason and have it all encounter, while attacking every round.
The other side of it is that, like sustained effects in general, it really becomes worth it in longer fights and is better the earlier you use it - so you do need to correctly predict that it will be a long fight and use it right away.
And if it does turn out all that OP, it probably shortens the fight.
If you think it's too much, it'd be easy to nerf, (like the above interpretation). Or, you could restrict it to minor-action sustains only (or restrict it from standard action sustains, or from use with sustains that include an attack roll, etc), or to sustaining powers already in effect when you use it. And/or require that you have actions available on your turn (everything becomes 'Sustain Free,' for the duration, I guess?), so Stun will break it as well as unconsciousness.
I suppose you should also be mindful of other things that would end the specific sustained powers that you're keeping up with it - like moving out of range or whatever.
Finally, at Epic, PCs are likely becoming famous and their enemies likely pretty serious, one of them occasionally having a counter/gotchya of some kind would't be unreasonable. Like a Dispel-type effect that ends one 'end-of-encounter arcane effect' or an aura that inflicts
n damage per effect you sustain while you (or any such effect) is in the aura, or whatever fiendish trick occurs to you. Not that such would 'balance' or 'nerf' the power, just that it could be an opportunity to make things interesting now and then.
Arcane
