I was just going to make a thread on this. Before people start downvoting you or me for mentioning lux buffs, they need to be reminded of the fact that riot is currently in amidst of buffing her. Her last buffs on pbe didn't go throw except the w cast time changed from 0 to 0.25 on her. The reason was that lux's designer felt that buffing her shield was not what the lux main's wanted as a buff.
First and foremost, lux sits as one of those champs that can easily be played at mid and as support. Ofcourse, she is struggling in both positions hence why the buffs are even sought, but most of us know that lux is currently very strong at low elo's but very weak at higher elos. She is also a better mid than a supp but personally i see lux as a damaging/utility support than as a mid champ.
I believe one of the biggest reason lux mid is not strong is because of her lack of farming potential, which more or less gets better after you get ludens. However, there are tons of other stuff you have to buy before and this usually means that lux has trouble farming the laning phase. If she decides to poke , she loses out on farming (fair enough) but the biggest issue with that is that her CD's her very high and so she gets punished really hard for missing her spells. Furthermore, eventhough her q can be used to farm, it puts her in danger of gank, and not to mention its high CD.
In addition, being a dominant skill shot player, any champ with mobility (looking at you yasuo, zed , leb, fizz, kat), all that can go mid, can easily counter her. But i guess that is one of the reasons why i love lux as a champ, i.e. a high risk, high reward champ. You miss her skillshots, you pay a big price but landing them can usually mean a kill or retreat of the enemy team.
I think the buff that OP mentioned is a buff i can see in the right direction for lux as a supp but it does nothing to help her weak early laning phase at mid. I think lux doesn't need MORE BURST but a little more consistent damage. When a lux is done and dusted with her combo, she will probbaly be unable to kill even a 5% health squishy. This is what frustrates the hell out of me. Enemy players call lux players as brain dead poke champ but they don't realize that after using her abilities, she becomes a sitting duck for decades. This is what i think promotes the stay back and poke play style of lux and which obviously doesn't work so well at higher elos as they know how to properly build and dodge xD.
I believe a simple solution would be to buff her passive in a way that it does no more burst than it already does but adds a little more consistent damage to help her after she has finished her combo. One way could be is to allow her passive to stack. So if i hit an enemy with Q and E (activated E), that would put 2 stacks on the enemy. The ult can also add into the stacks or consume one stack and replace it with another (like it currently does) and hence no change in the overall stacks, depending on how strong it'll make lux to have too many stacks. AA'ing the person consumes 1 stack only (so that she doesn't get anymore burst than she currently has) and that means lux will have another stack that she can AA again to proc. As for helping her farm at mid, i believe any way of increasing her procing passive damage to minions can help immensely.
I would like riot to keep her as a utility/damage dealing champs that i love to play. We already have zyra, brand and velk as stupidly damage dealing supp.
since their passives support their poke play style. She has to auto to proc it however since she is a ranged/poke mage getting in auto range often spells her own death or a bad trade. She might be able to use it in lane a few times but other than that you usually only use ult to proc her passive.
is, but lux support is not REMOTELY weak if picked into the proper enemy support.
has to actually engage to make allies proc her passive, in lane, you could have a 
spamming E, and a long-ranged adc like 
proc it for her without taking any risk, and it would just make her even more obnoxious