i see it also when 2.0 hits their will be arcanist everywhere, and parties will most likely have 5-6 acn in them just from the addition of the class. LL will be very packed from everyone being acn so hopefully 2.0 servers can handle it. And the reasons why their are going to be many acn around are:

1) all the ppl having every class at 50 will level it just to have it at 50
2) all the ppl who wanted to play it from the start and couldnt
3) all the ppl who are just curious and want to try it
4) all the newcomers to take into account that will play it

Now going along with what biggs said about musketeer being realeased with arcanist at 2.0 start will help balance the influx of everyone being on one class. but LL will still be packed and probably become the 2.0 verison of uldah from 1.0